Anatomy & Physiology

The Nervous SystemThe Nervous System

Organization of the Nervous System Central Nervous System (CNS):Central Nervous System (CNS): consists of the consists of the

brain and spinal cord, which occupy the dorsal brain and spinal cord, which occupy the dorsal body cavity.body cavity.

Peripheral Nervous System (PNS):Peripheral Nervous System (PNS): the part of the part of the nervous system outside the CNS, consisting the nervous system outside the CNS, consisting mainly of the nerves that extend from the brain mainly of the nerves that extend from the brain and spinal cord.and spinal cord.

A) A) Spinal nervesSpinal nerves- carry impulses to and from the - carry impulses to and from the spinal cord.spinal cord.

B) B) Cranial nervesCranial nerves- carry impulses to and from the - carry impulses to and from the brain.brain.

Peripheral Nervous System (PNS)

The PNS has two functional subdivisions:The PNS has two functional subdivisions: 1) Sensory (Afferent) division- consists of nerve 1) Sensory (Afferent) division- consists of nerve

fibers that convey impulses to the central nervous fibers that convey impulses to the central nervous system from sensory receptors located throughout system from sensory receptors located throughout the body.the body.

a) Somatic afferent fibers- convey impulses from a) Somatic afferent fibers- convey impulses from the skin, skeletal muscles, and jointsthe skin, skeletal muscles, and joints

b) Visceral afferent fibers- sensory fibers b) Visceral afferent fibers- sensory fibers transmitting impulses from the visceral organstransmitting impulses from the visceral organs

PNS, cont. 2) Motor (efferent) division- transmits impulses from 2) Motor (efferent) division- transmits impulses from

the CNS to effector organs, the muscles and glands.the CNS to effector organs, the muscles and glands. The motor division has two main parts:The motor division has two main parts: a) Somatic nervous system- composed of somatic a) Somatic nervous system- composed of somatic

nerve fibers that conduct impulses from the CNS to nerve fibers that conduct impulses from the CNS to skeletal muscles (voluntary)skeletal muscles (voluntary)

b) Autonomic nervous system- consists of visceral b) Autonomic nervous system- consists of visceral motor nerve fibers that regulate the activity of smooth motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands.muscles, cardiac muscles, and glands.

1. Sympathetic- mobilizes body systems during emergencies1. Sympathetic- mobilizes body systems during emergencies 2. Parasympathetic- conserves energy, promotes 2. Parasympathetic- conserves energy, promotes

nonemergency functions.nonemergency functions.

Central Nervous System (CNS)

Consists of the brain and spinal cordConsists of the brain and spinal cord Receives messages from the bodyReceives messages from the body Sends out signals to the body in responseSends out signals to the body in response

CENTRAL NERVOUS SYSTEM

Organization of the Brain

The brain is part of the CNSThe brain is part of the CNS Consists of:Consists of: Cerebral hemispheres (right and left)Cerebral hemispheres (right and left) Diencephalon (hypothalamus, thalamus)Diencephalon (hypothalamus, thalamus) Brain stem ( midbrain, pons, and medulla)Brain stem ( midbrain, pons, and medulla)

Tissue pattern in the CNS Spinal cord: central Spinal cord: central

cavity surrounded cavity surrounded by a gray matter core. by a gray matter core.

Outer layer is white Outer layer is white matter (myelinated matter (myelinated fiber tracts).fiber tracts).

Brain has the same Brain has the same basic design with basic design with areas of gray matter.areas of gray matter.

Ventricles of the Brain Ventricles are spaces in the brain that arose from the Ventricles are spaces in the brain that arose from the

neural tube.neural tube. There are four ventricles, each filled with There are four ventricles, each filled with

cerebrospinal fluid (CSF).cerebrospinal fluid (CSF). Lateral ventriclesLateral ventricles are in the cerebral hemispheres, are in the cerebral hemispheres,

separated by a thin membrane (septum pellucidum).separated by a thin membrane (septum pellucidum). The The third ventriclethird ventricle is connected to the lateral is connected to the lateral

ventricles by the interventricular foramen.ventricles by the interventricular foramen. The The fourth ventriclefourth ventricle is in the brain stem and is in the brain stem and

connects with the central canal of the spinal cord connects with the central canal of the spinal cord (also connected to the third ventricle by the cerebral (also connected to the third ventricle by the cerebral aqueduct.aqueduct.

Hydrocephalus The fluid produced by the The fluid produced by the

ventricles must circulate ventricles must circulate and drain.and drain.

If fluid is overproduced, If fluid is overproduced, or cannot drain properly, it or cannot drain properly, it builds up causing enlarged builds up causing enlarged skull and intracranial skull and intracranial pressure.pressure.

Hydrocephalus can be Hydrocephalus can be treated by inserting a treated by inserting a straw-like shunt to help straw-like shunt to help drain the CSF.drain the CSF.

Cerebral Hemispheres Cerebral hemispheres form the superior part of the Cerebral hemispheres form the superior part of the

brain, making up about 83% of total brain mass.brain, making up about 83% of total brain mass. Surface is marked by elevated ridges of tissue Surface is marked by elevated ridges of tissue

called gyri separated by shallow grooves called called gyri separated by shallow grooves called sulci (singular forms are gyrus and sulcus).sulci (singular forms are gyrus and sulcus).

Deeper grooves called fissures separate larger Deeper grooves called fissures separate larger regions of the brain; longitudinal fissure separates regions of the brain; longitudinal fissure separates the cerebral hemispheres, transverse fissure the cerebral hemispheres, transverse fissure separates the cerebral hemispheres from the separates the cerebral hemispheres from the cerebellum.cerebellum.

Lobes of the Brain Deep sulci divide each hemisphere into five Deep sulci divide each hemisphere into five

lobes: frontal, temporal, occipital, and lobes: frontal, temporal, occipital, and insula– all but the last named after the insula– all but the last named after the cranial bones that cover them.cranial bones that cover them.

The central sulcus separates the frontal lobe The central sulcus separates the frontal lobe from the parietal lobe.from the parietal lobe.

The parieto-occipital sulcus separates the The parieto-occipital sulcus separates the occipital and parietal lobes.occipital and parietal lobes.

Lobes of the brain, cont.

The insula is buried deep within the lateral The insula is buried deep within the lateral sulcus, and is covered by parts of the sulcus, and is covered by parts of the temporal, parietal, and frontal lobes.temporal, parietal, and frontal lobes.

The lateral sulcus outlines the temporal lobe The lateral sulcus outlines the temporal lobe and separates it from the parietal lobe and and separates it from the parietal lobe and frontal lobes.frontal lobes.

Cerebral Cortex The cerebral cortex is the area that carries The cerebral cortex is the area that carries

out the processes of the “conscious mind”.out the processes of the “conscious mind”. It enables us to be aware of our sensations, It enables us to be aware of our sensations,

to communicate, remember, understand, to communicate, remember, understand, and to initiate voluntary movements.and to initiate voluntary movements.

Composed of gray matter (neuron cell Composed of gray matter (neuron cell bodies, dendrites, and unmyelinated axons).bodies, dendrites, and unmyelinated axons).

Accounts for about 40% brain mass.Accounts for about 40% brain mass.

Cerebral cortex, cont.

Contains three functional areas:Contains three functional areas: 1) Motor areas that control voluntary motor 1) Motor areas that control voluntary motor

functionsfunctions 2) Sensory areas that provide conscious 2) Sensory areas that provide conscious

awareness of sensationawareness of sensation 3) Association areas that integrate a wide 3) Association areas that integrate a wide

range of information for purposeful actionrange of information for purposeful action

Cerebral cortex, cont.

Each hemisphere is chiefly concerned with Each hemisphere is chiefly concerned with the sensory and motor functions of the the sensory and motor functions of the opposite side of the body.opposite side of the body.

The two hemispheres are not equal in The two hemispheres are not equal in function; each is partially specializedfunction; each is partially specialized

Conscious behavior involves the entire Conscious behavior involves the entire cortex; no functional area acts alonecortex; no functional area acts alone

Motor areas Cortical areas controlling motor functions lie in Cortical areas controlling motor functions lie in

the posterior part of the frontal lobes.the posterior part of the frontal lobes. 1) 1) Primary (somatic) motor cortex-Primary (somatic) motor cortex- allow allow

conscious control of skeletal muscles, skilled and conscious control of skeletal muscles, skilled and precise movements.precise movements.

2) 2) Premotor cortex-Premotor cortex- Controls learned motor skills Controls learned motor skills with patterns, such as playing an instrument. Also with patterns, such as playing an instrument. Also involved in planning movements.involved in planning movements.

Motor areas, cont.

Broca’s area-Broca’s area- lies anterior to the premotor lies anterior to the premotor area. Involved in speech, including motor area. Involved in speech, including motor control of muscles involved in speech control of muscles involved in speech production and mental preparation for production and mental preparation for speaking.speaking.

Frontal eye field-Frontal eye field- Controls voluntary Controls voluntary movement of the eyes.movement of the eyes.

Sensory Areas Unlike the motor areas, which are confined to Unlike the motor areas, which are confined to

the frontal lobe cortex, areas concerned with the frontal lobe cortex, areas concerned with conscious awareness of sensation occur in the conscious awareness of sensation occur in the parietal, temporal, and occipital lobes.parietal, temporal, and occipital lobes.

1) Primary somatosensory cortex- located in 1) Primary somatosensory cortex- located in the postcentral gyrus of the parietal lobe. the postcentral gyrus of the parietal lobe. Receives information from sensory receptors in Receives information from sensory receptors in the skin from proprioceptors in skeletal the skin from proprioceptors in skeletal muscles. Identifies body region being muscles. Identifies body region being stimulated (spatial discrimination).stimulated (spatial discrimination).

Sensory Areas, cont. 2) Somatosensory Association cortex- lies 2) Somatosensory Association cortex- lies

posterior to the primary somatosensory posterior to the primary somatosensory cortex.cortex.

Function is to integrate different sensory Function is to integrate different sensory inputs (temperature, pressure, etc.) to inputs (temperature, pressure, etc.) to produce a comprehensive understanding o produce a comprehensive understanding o an object being felt.an object being felt.

Someone with damages to this area would Someone with damages to this area would not be able to recognize objects without not be able to recognize objects without looking at them.looking at them.

Visual areas Primary visual cortex- located on the Primary visual cortex- located on the

posterior tip of the occipital lobe.posterior tip of the occipital lobe. Largest of all cortical sensory areas, the Largest of all cortical sensory areas, the

primary visual cortex receives visual primary visual cortex receives visual information that originates on the retinas of information that originates on the retinas of the eyes.the eyes.

The visual association area interprets visual The visual association area interprets visual stimuli (color, form, movement) based on stimuli (color, form, movement) based on past visual experiences.past visual experiences.

Auditory areas Primary auditory cortex is located in the Primary auditory cortex is located in the

superior part of the temporal lobe.superior part of the temporal lobe. Sound energy stimulating receptors in the Sound energy stimulating receptors in the

inner ear transmits impulses to the primary inner ear transmits impulses to the primary auditory cortex, where they are related to auditory cortex, where they are related to pitch, rhythm, and loudness.pitch, rhythm, and loudness.

The auditory association area interprets The auditory association area interprets sound stimuli, identifying it based on past sound stimuli, identifying it based on past experience.experience.

Olfactory area

Olfactory (smell) cortex is found in small Olfactory (smell) cortex is found in small areas in the frontal lobe, above the orbits.areas in the frontal lobe, above the orbits.

Afferent fibers from smell receptors in the Afferent fibers from smell receptors in the superior nasal cavities send impulses along superior nasal cavities send impulses along olfactory tracts that are relayed to the olfactory tracts that are relayed to the olfactory cortex.olfactory cortex.

Results in conscious awareness of odors.Results in conscious awareness of odors.

Gustatory area/Vestibular area The gustatory (taste) cortex is involved in The gustatory (taste) cortex is involved in

the perception of taste stimuli.the perception of taste stimuli. Located in the parietal lobe just deep to the Located in the parietal lobe just deep to the

temporal lobe.temporal lobe. The vestibular (equilibrium) cortex is The vestibular (equilibrium) cortex is

located deep to the temporal lobe (insula). located deep to the temporal lobe (insula). Responsible for conscious awareness of Responsible for conscious awareness of balance.balance.

The Diencephalon

Consists of three paired structures: the Consists of three paired structures: the thalamus, hypothalamus, and epithalamus.thalamus, hypothalamus, and epithalamus.

Each is surrounded by cerebral Each is surrounded by cerebral hemispheres.hemispheres.

These are gray matter areas enclosing the These are gray matter areas enclosing the third ventricle.third ventricle.

Thalamus Makes up 80% of the diencephalon. Contains Makes up 80% of the diencephalon. Contains

about a dozen nuclei, named for their relative about a dozen nuclei, named for their relative locations.locations.

Major relay station for sensory impulses Major relay station for sensory impulses ascending to the sensory cortex.ascending to the sensory cortex.

Transmits inputs from subcortical motor nuclei Transmits inputs from subcortical motor nuclei and the cerebellum traveling to the cerebral motor and the cerebellum traveling to the cerebral motor cortex.cortex.

Transmits impulses traveling to association Transmits impulses traveling to association cortices from lower centers.cortices from lower centers.

Hypothalamus Positioned below the thalamus, caps the top of the Positioned below the thalamus, caps the top of the

brainstembrainstem Important autonomic nervous system control center Important autonomic nervous system control center

and part of the limbic system.and part of the limbic system. Maintains water balance and regulates thirst, eating Maintains water balance and regulates thirst, eating

behavior, gastrointestinal activity, body temperature, behavior, gastrointestinal activity, body temperature, and activity of the anterior pituitary gland.and activity of the anterior pituitary gland.

Mammilary bodies that bulge anteriorly from the Mammilary bodies that bulge anteriorly from the hypothalamus are relay stations in the olfactory hypothalamus are relay stations in the olfactory pathways.pathways.

Epithalamus Most dorsal portion of the diencephalon, Most dorsal portion of the diencephalon,

forming the roof of the third ventricle.forming the roof of the third ventricle. Consists of the pineal gland and choroid Consists of the pineal gland and choroid

plexus of the third ventricle.plexus of the third ventricle. The pineal gland secretes a hormone, The pineal gland secretes a hormone,

melatonin, which is thought to help regulate melatonin, which is thought to help regulate sleep-wake cycles and some aspects of sleep-wake cycles and some aspects of mood.mood.

Homeostatic Imbalance: Hypothalamus

A disturbance in the hypothalamus can A disturbance in the hypothalamus can cause a number of disorders in body cause a number of disorders in body homeostasis:homeostasis:

Severe body wasting or obesitySevere body wasting or obesity Sleep disturbancesSleep disturbances DehydrationDehydration Emotional disturbancesEmotional disturbances