nervous system part 2
TRANSCRIPT
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Mikhail Ness M. Buhay, MD
Nervous SystemPart 2
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The Spinal Cord and Spinal Nerves
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Spinal Cord Structure: Protection and Coverings◼ Vertebrae
◼ Spinal meninges
❑ Three layers of connective tissue
◼ Dura mater
◼ Arachnoid mater
◼ Pia mater
❑ Continuous with cranial meninges
◼ Cerebrospinal fluid (CSF)
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Spinal Meninges and Spaces◼ Epidural space
❑ Between the vertebrae and dura mater
◼ Dura mater- tough mother
❑ Thick strong layer, dense irregular connective tissue
❑ Extends to vertebra S2 (well beyond spinal cord)
◼ Subdural space❑ Contains interstitial fluid
◼ Arachnoid mater: resembles spider’s web❑ Thin, avascular covering of loosely
arranged collagen and elastic fibers
❑ Extends into subarachnoid space
◼ Subarachnoid space ❑ CSF circulates in this space
◼ Pia mater ❑ Thin, delicate layer
❑ Adheres to surface spinal cord (and brain)
❑ Contains blood vessels
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Spinal Meninges and Spaces◼ Denticulate ligaments
❑ Thickenings of pia mater
❑ Fuse with arachnoid mater and dura mater
❑ Between the anterior and posterior nerve roots of spinal nerves
❑ Suspend the spinal cord at the middle
❑ Protect the spinal cord from sudden displacement →shock
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Spinal Tap◼ Spinal tap/Lumbar
puncture❑ Long hollow needle inserted
into the SA space
◼ Spinal cord – ends at L2 (superior border)
◼ Spinal meninges – extend to S2
◼ Between L2 and S2◼ (+) spinal meninges◼ (–) spinal cord
◼ Adults – (L3-L4) or (L4-L5)❑ Safe access to the SA
space
❑ Supracristal line –passes L4 spinous process
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External Anatomy of Spinal Cord◼ SC is roughly oval
◼ Adults: Extends from medulla of brain to L2 superior border
◼ Newborn: Extends up to L3/L4
◼ Enlargements: cervical (C4-T1) and lumbar regions (T9-T12)❑ Points of origins of nerves to upper and lower limbs
◼ Conus medullaris – SC ends as a tapering, conical structure❑ L1-L2 intervertebral disc
◼ Filum terminale – arise from conus medullaris❑ Extensions of the pia mater; fuses with the arachnoid and dura mater❑ Anchors SC to the coccyx
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External Anatomy of Spinal Cord◼ Spinal nerves – paths of communication bet. SC and body region
❑ 31 pairs of spinal nerves emerge from the intervertebral foramina❑ Cervical – 8 (C1-C8)❑ Thoracic – 12 (T1-T12)❑ Lumbar – 5 (L1-L5)❑ Sacral – 5 (S1-S5)❑ Coccygeal – 1 (Co1)
◼ Roots – bundles of axons❑ Connect each spinal nerve to a segment of the cord by even smaller bundles of axons
(rootlets)
◼ Posterior (dorsal) root & rootlets – contain only sensory axons
❑ Each posterior root has a swelling, the posterior (dorsal) root ganglion – contains the cell bodies of sensory neurons.
◼ Anterior (ventral) root & rootlets – contain only motor axons
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External Anatomy of Spinal Cord◼ Spinal nerves – branch from the SC
❑ Pass laterally and exit thru the intervertebral foramina
◼ SC shorter than vertebral column❑ Lumbar, sacral and coccygeal regions – do not leave the vertebral
column at the same level they exit the cord
❑ Their roots angle inferiorly alongside the filum terminale
◼ Cauda equina (horse’s tail)❑ Extends inferior to end of spinal cord
❑ Consists of roots of lumbar, sacral and coccygeal spinal nerves
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Gross Anatomy of Spinal Cord• The spinal cord extends
from the medulla oblongata of the brain to the superior border of the second lumbar vertebra.
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REVIEW: Collections of Nervous Tissue
◼ Clusters of neuron cell bodies
❑Ganglion: cluster of cell bodies in PNS
❑Nucleus: cluster of cell bodies in CNS
◼ Bundles of axons
❑Nerve: bundle of axons in PNS
❑Tract: bundle to axons in CNS
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Internal Anatomy of the Spinal Cord◼ A transverse section of the spinal cord reveals regions of white matter that surround an
inner core of gray matter
◼ Gray matter forms “H” (or “butterfly”) ❑ Consists of dendrites and cell bodies of neurons, unmyelinated axons, and neuroglia.
❑ Three horns (regions) on each side
◼ Posterior (dorsal) gray horns: contain sensory neurons and interneurons◼ Sensory neuron cell bodies – located in the posterior (dorsal) root ganglion of a spinal nerve
◼ Anterior (ventral) gray horns: contain somatic motor nuclei◼ Somatic motor nuclei – clusters of cell bodies of somatic motor neurons that provide nerve
impulses for contraction of skeletal muscles
◼ Lateral gray horns: contain autonomic motor nuclei◼ Located between anterior and posterior gray horns; only in thoracic and upper lumbar SC
segments◼ Autonomic motor nuclei – clusters of cell bodies of autonomic motor neurons that regulate the
activity of cardiac muscle, smooth muscle, and glands
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Internal Anatomy of the Spinal Cord
◼ White matter (surrounds gray “H”)
❑ Consists of white columns, myelinated axons of neurons
◼Posterior (dorsal), anterior (ventral), and lateral white columns◼ Contain tracts (bundles of axons)
❑Sensory (Ascending) tracts: carry nerve impulses ascending to brain
❑Motor (Descending) tracts: carry nerve impulses descending from brain
◼ Sensory and Motor tracts of the SC are continuous with the tracts of the brain.
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Internal Structure of Spinal Cord• The posterior gray horn
contains axons of sensory neurons and cell bodies of interneurons; the lateral gray horn contains cell bodies of autonomic motor neurons; and the anterior gray horn contains cell bodies of somatic motor neurons.
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Internal Structure of Spinal Cord
H -crossbarEntire SC; CSF; 4th Ventricle
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Internal Anatomy of the Spinal Cord
◼ Nucleus/Nuclei❑ In the gray matter of the CNS (brain and SC)
❑ Functional groups formed by clusters of neuronal cell bodies
◼ Sensory nuclei – receive input from receptors via sensory neurons
◼ Motor nuclei – provide output to effector tissues via motor neurons
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Internal Structure of Spinal Cord
• The posterior gray horn contains axons of sensory neurons and cell bodies of interneurons; the lateral gray horn contains cell bodies of autonomic motor neurons; and the anterior gray horn contains cell bodies of somatic motor neurons.
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Spinal Nerves
◼ 31 pairs❑ Named according to level of vertebra from which they emerge
❑ C1-C8, T1-T12, L1-L5, S1-S5, 1 coccygeal
❑ Emerge from spinal cord through intervertebral foramina
❑ Connect the CNS to the sensory receptors, muscles, and glands in all parts of the body
◼ Nerves attached to spinal cord by 2 roots
❑ Dorsal root: made of axons of sensory neurons◼ Dorsal root ganglion: swelling containing cell bodies of sensory neurons
❑ Ventral root: composed of axons of motor neurons◼ Both somatic motor and autonomic motor
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Spinal Nerve Composition
◼ Formed by 2 spinal nerve roots
◼ Spinal nerve is a mixed nerve:❑ Formed from dorsal root (sensory) and ventral root (motor) root
◼ Connective tissue coverings of Spinal Nerves❑ Each spinal nerve and cranial nerve consists of many individual axons
and contains layers of protective connective tissue coverings
❑ Individual axons wrapped in endoneurium (innermost layer)
❑ Axons grouped in fascicles wrapped in perineurium (middle layer)
❑ Outer covering = epineurium (outermost layer)
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Spinal Nerve Composition
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Distribution of Spinal Nerves
◼ Spinal nerves divides into several branches (rami) after pass through intervertebral foramina
◼ Posterior ramus – serves the deep muscles and skin of the posterior surface of the trunk
◼ Anterior ramus – serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk
◼ Meningeal branch – reenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges
◼ Rami communicantes◼ Some join with branches from neighboring nerves to form plexuses (network of
axons)
◼ Nerve names relate to region innervated
◼ Spinal nerves T2-T12 do not form plexuses❑ They are called intercostal nerves/thoracic nerves – directly connect to the structures they
supply in the intercostal spaces
❑ Supply abdominal muscles, skin of chest and back, and muscles between ribs.
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Plexuses
◼ Cervical plexus❑ C1-C4 roots + C5
contributions
❑ Supplies the skin and muscles of the head, neck, and superior part of the shoulders and chest, diaphragm
❑ Important nerves: phrenic to diaphragm
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Plexuses
◼ Brachial plexus ❑ Formed by roots of
spinal nerves from C5-C8 and T1
❑ Supplies upper limbs + some neck and shoulder muscles
❑ Important nerves: radial, ulnar, median
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Plexuses
◼ Lumbar plexus❑ Formed by the anterior
rami spinal nerve roots L1-L4
❑ Supplies anterolateral abdominal wall, external genitalia, and part of lower limbs
❑ Important nerves: femoral (to anterior thigh: quads)
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Plexuses
◼ Sacral plexus❑ Sacral plexus formed by the
anterior rami spinal nerve roots of L4-L5 and S1-S4
❑ Supplies buttocks, perineum, and most of lower limbs
❑ Sciatic nerve – largest nerve in the body
❑ Important nerves: gluteal, sciatic (to posterior thigh and all of leg and foot)
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Plexuses
◼ Coccygeal plexus❑ Formed by the anterior
rami spinal nerve roots of
S4-S5 and the coccygeal
nerves
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Dermatomes
◼ A dermatome is an area of skin that provides
sensory input to the CNS via the posterior roots of
one pair of spinal nerves or via the trigeminal (V)
nerve.
◼ The nerve supply in adjacent dermatomes
overlaps somewhat.
◼ Knowing which spinal cord segments supply each
dermatome makes it possible to locate damaged
regions of the spinal cord.
◼ If the skin in a particular region is stimulated but
the sensation is not perceived, the nerves
supplying that dermatome are probably damaged.
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The Brain and Cranial Nerves
Mikhail Ness M. Buhay, MD
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◼ The brain and spinal cord develop from the ectodermal neural tube
◼ The anterior part of the neural tube expands, along with the associated neural crest tissue. Constrictions in this expanded tube soon appear, creating three regions called primary brain vesicles: ◼ Prosencephalon◼ Mesencephalon◼ Rhombencephalon
Brain
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Brain: Major Parts◼ Brain stem: continuous with spinal cord
❑ Medulla oblongata, pons, midbrain
◼ Diencephalon: superior to brain stem
❑ Thalamus, hypothalamus, and pineal gland
◼ Cerebrum: largest part and most superior
❑ Surface covered with gray matter: cortex
❑ Deep to cortex is cerebral white matter
◼ Cerebellum: posterior and inferior
❑ Means “little brain”
◼ Cranial meninges: dura mater, arachnoid mater, and pia mater
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Brain: Major Parts
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Brain: Major Parts
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Brain Blood Flow and the Blood-Brain Barrier (BBB)◼ Internal carotid & vertebral arteries →
brain
◼ Dural venous sinuses → internal jugular veins → heart
◼ Requires 20% of the body’s O2 supply❑ 4 min lack → permanent damage
◼ Requires continuous glucose supply
◼ Protected by blood-brain barrier❑ Allows passage of lipid soluble materials: O2,
CO2, alcohol, anesthetic agents
❑ But controls entry of most harmful materials
◼ Created by tight capillaries and astrocytes
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Cerebrospinal Fluid (CSF)
◼ CSF is a clear, colorless liquid composed primarily of water that protects the brain and spinal cord from chemical and physical injuries.
◼ It also carries small amounts of oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia.
◼ CSF continuously circulates through cavities in the brain and spinal cord and around the brain and spinal cord in the subarachnoid space
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Cerebrospinal Fluid (CSF)
◼ Formed in the 4 ventricles of brain❑ Lateral (#1 and 2) → 3rd → 4th ventricle
❑ Formed in choroid plexuses◼ By filtration and secretion of blood plasma
◼ In specialized capillary networks (covered by ependymal cells) in walls of ventricles
◼ Pathway❑ Through 4 ventricles → central canal of spinal cord and within
subarachnoid space →
❑ Reabsorbed through arachnoid villi into blood in superior sagittal sinus
◼ Cushions brain and provides nutrients
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Locations of ventricles within a “transparent” brain.
• One interventricular foramen on each side connects a lateral ventricle to the third ventricle, and the aqueduct of the midbrain connects the third ventricle to the fourth ventricle.
• Ventricles are cavities within the brain that are filled with cerebrospinal fluid.
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Cerebrospinal Fluid (CSF)
• CSF is formed from blood plasma by ependymal cells that cover the choroid plexuses of the ventricles.
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Cerebrospinal Fluid (CSF)
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Cerebrospinal Fluid (CSF)
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Brain Stem: Medulla Oblongata
◼ Most inferior part of brainstem❑ White matter connects spinal cord
and other parts of brain
◼ Contains vital nuclei❑ Cardiovascular center
◼ Regulates heart rate, blood pressure
❑ Medullary rhythmicity area ◼ Adjusts respiratory rhythm
◼ Other sensory and reflex motor areas
◼ Cranial nerves VIII-XII attached here
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Brain Stem: Pons
◼ Serves as a “bridge”❑ Connects medulla to midbrain
and above
❑ Contains ascending and descending tracts
❑ Connects left and right sides of cerebellum
◼ Contains nuclei ❑ Motor relays from cerebrum to
cerebellum
❑ Helps control breathing
❑ Cranial nerves V-VIII attached here
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Brain Stem: Midbrain
◼ Connects pons to diencephalon❑ Large tracts: cerebral peduncles
◼ Nuclei: ❑ Substantia nigra: related to
Parkinson disease❑ Red nuclei: help coordinate
movements❑ Origin of cranial nerves III and IV
(control eye movements)❑ Superior colliculi: nuclei involved in
◼ Scanning eye movements ◼ Responses to visual stimuli
❑ Inferior colliculi: responses to auditory input
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Brain Stem
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Midbrain
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Reticular Formation
◼ Netlike arrangement of gray and white matter
◼ Contains ascending and descending tracts
◼ Ascending part = reticular activating system (RAS)
❑ Carries sensory pathways to cerebral cortex
❑ Helps maintain consciousness
❑ Helps induce sleep
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Reticular Formation
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Reticular Formation
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Diencephalon
◼ Thalamus: major sensory relay center❑ Also motor, autonomic, and consciousness functions
◼ Hypothalamus: lies inferior to thalamus❑ Control of pituitary and hormone production
❑ Works with ANS regulating many viscera
❑ Involved with feelings and behavior patterns
❑ Regulation of eating, drinking, fluid levels
❑ Control of body temperature
❑ Regulation of circadian rhythms, sleep, waking
◼ Pineal gland: secretes melatonin❑ Controls sleep, biological clock
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Diencephalon
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Cerebellum
◼ Location: posterior to medulla and pons, inferior to
cerebrum
❑ Attached to brain stem by cerebellar peduncles
◼ Structure:
❑ Two cerebellar hemispheres
❑ Cerebellar cortex: gray matter
❑ Tree-like appearance (seen in sagittal section) of white matter
and gray nuclei
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Cerebellum
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Cerebellum
◼ Functions❑ Receives wide range of sensory input from muscles, joints,
tendons, eyes, inner ears
❑ Compares actual movements with intended ones
❑ Helps produce smooth, coordinated movements
❑ Helps execute skilled motor activities
❑ Regulates posture and balance
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Cerebrum: Structure
◼ Cerebral cortex
◼ Internal white mater
◼ Deep gray nuclei
◼ Surface folds of cerebral cortex: gyri
◼ Grooves between gyri: sulci
◼ Longitudinal fissure: divides cerebrum into left and right hemispheres
◼ Hemispheres connected by corpus collosum
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Cerebrum: Structure
◼ Each hemisphere has 4 lobes❑ Frontal, parietal, temporal, occipital
❑ Central sulcus separates frontal, parietal
❑ Precentral gyrus anterior to sulcus: primary motor area
❑ Postcentral gyrus: primary somatosensory area
◼ Deep gray nuclei: basal ganglia❑ Globus pallidus, putamen, caudate nucleus
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Cerebrum
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Cerebrum
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Limbic System
◼ Ring of structures on inner border of cerebrum and floor of
diencephalon
◼ Called “emotional brain”: plays primary role in pain,
pleasure, anger, affection and in behavior
◼ Involuntary activity related to survival
◼ Important in memory development
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Limbic System
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Functional Areas of Cerebral Cortex
◼ Specialized areas in specific regions of cerebral cortex
◼ Sensory areas receive input → perception
◼ Motor areas → initiate movements
◼ Associative areas → complex integration: memory, emotion, reasoning, judgment
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Sensory Areas
◼ Primary somatosensory area: postcentral gyrus❑ Input includes: touch, proprioception, pain, itching, tickle, temperature
◼ Primary visual area: occipital lobe
◼ Primary auditory area: temporal lobe
◼ Primary gustatory (taste) area: base of postcentral gyrus
◼ Primary olfactory (smell) area: medial aspect of temporal lobe
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Motor Areas
◼ Located anterior to central sulcus
◼ Primary motor area: precentral gyrus
◼ Broca’s speech area
❑ Interacts with premotor area and primary motor area to regulate
breathing and speech muscles
❑ Is in left hemisphere in 97% of persons
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Association Areas
◼ Adjacent to sensory and motor areas and connected via association tracts
◼ Integrate and interpret information
◼ Examples❑ Somatosensory association area
◼ Posterior to primary somatosensory area
◼ Integrates sensation: exact shape and texture of object compared with stored memories
❑ Wernicke’s area: left temporal, parietal lobes◼ Interprets meaning of speech: words → thoughts
◼ Right hemisphere adds emotional content
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Cerebrum: Functional Areas
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Somatic Sensory Pathways
◼ Relay sensory information from periphery to cerebral cortex
◼ 3 neurons in each pathway
❑ Cell body #1 in dorsal root ganglion
❑ Cell body #2 in spinal cord or brain stem
❑ Cell body #3 in thalamus; axon extends to cerebral cortex (somatosensory area in postcentral gyrus)
◼ Most sensory input to right side of body reaches left side of brain (and vice versa)
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Somatic Sensory Pathways
◼ Posterior column - medial lemniscus pathway senses
❑ Fine touch: body location, texture, size
❑ Proprioception: position and motion of body parts
❑ Vibrations: fluctuating touch stimuli
◼ Spinothalamic pathways❑ Anterior and lateral spinothalamic tracts
❑ Relay impulses for pain, tickle, itch, hot, and cold sensations
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Somatic Sensory Pathways• The posterior column–medial lemniscus
pathway conveys nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head to the cerebral cortex.
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Somatic Motor Pathways
◼ Signals come from
❑ Upper motor neurons: via corticospinal tracts
❑ Basal ganglia: help with muscle tone
❑ Cerebellum: coordination
❑ Sensory neurons or interneurons via reflexes
◼ Impulses activate lower motor neurons
❑ Cell bodies in anterior gray of spinal cord
❑ Axons → ventral root → spinal nerve → muscle → voluntary
movements
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Somatic sensory and somatic motor maps in the cerebral cortex, right hemisphere.
• (a) Primary somatosensory area (postcentral gyrus) and (b) primary motor area (precentral gyrus) of the right cerebral hemisphere. The left hemisphere has similar representation. (After Penfield and Rasmussen.)
• Each point on the body surface maps to a specific region in both the primary somatosensory area and the primary motor area.
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Lateralization
◼ Brain controls opposite side of the body: all sensory and motor pathways cross in CNS
❑ Left side of the brain controls right side of body
❑ Right side of brain controls left side of body
◼ Left hemisphere important for spoken and written language, numerical and scientific skills, and reasoning
◼ Right side more involved with spatial and pattern recognition and emotional content
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Memory
◼ Process for storing and retrieving information
◼ Involves structural and functional changes
◼ Involves association areas, parts of limbic system, and diencephalon
◼ Skill memory also involves cerebellum and basal ganglia
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Cranial Nerves
I. Olfactory: special sensory—smell
II. Optic: special sensory—vision
III.Oculomotor: motor—control of eye movements
IV.Trochlear: motor—control of eye movements
V. Trigeminal: mixed
❑General sensory: touch, pain, pressure, hot, cold in face
❑Motor: to muscles used for chewing
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Cranial Nerves
VI.Abducens: motor—control of eye movements
VII.Facial: mixed
❑ Special sensory (taste) from anterior of tongue
❑ Motor to muscles of facial expression, tear glands, and some salivary glands
VIII.Vestibulocochlear: special sensory—ear
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Cranial Nerves
IX.Glossopharyngeal: mixed
❑ Sensory for posterior of tongue, pharynx, and palate; blood
pressure
❑ Motor to pharyngeal muscles (swallowing), salivary gland
(parotid
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Cranial Nerves
X. Vagus: mixed (the major parasympathetic nerve)
❑ Sensory from pharynx, ear, diaphragm, visceral organs in
thoracic and abdominal cavities
❑ Motor to palatal and pharyngeal muscles (swallowing and
voice); to viscera in thoracic and abdominal cavities
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Cranial Nerves
XI.Accessory: motor to voluntary muscles including
sternocleidomastoid and trapezius (move head,
shoulders)
XII.Hypoglossal: motor to tongue (swallowing and speech)
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Aging
◼ Rapid brain growth during first few years of life❑ Due to increase in size of neurons and proliferation of neuroglia
❑ Increase in development of dendritic branches and synaptic
contacts
◼ From early adulthood through old age:
❑ Decline in brain mass
❑ Fewer synaptic contacts brain function
❑ Some decrease in brain function
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Mikhail Ness M. Buhay, MD
ThankYou!