Exercise 17

Histology of Nervous Tissue

Introduction 2 principle cell populations:

Neuroglia- also called glial cells In central nervous system (CNS), they are astrocytes,

oligodendrocytes, microglia, ependymal cells In peripheral nervous system (PNS), they are Schwann

cells, satellite cells Brace, protect & insulate neurons Act as phagocytes Myelinate neuronal extensions Participate in capillary/neuron exchanges Control chemical environment around neurons NOT capable of generating or transmitting nerve

impulses

Introduction (continued) Neurons

Basic functional unit of nervous tissue Highly specialized to transmit nerve impulses from

one part of the body to another Neuron anatomy

Cell body Found in CNS in clusters called nuclei, outside CNS in

clusters called ganglia Make up the grey matter of the nervous system Large, rounded nucleus surrounded by neuroplasm

(cytoplasm)

Neuron Anatomy (continued)

2 types of neuron processes: Dendrites- receptive regions; they receive

nerve impulses Axons- generate & conduct nerve impulses

Know figures 17.1, 17.2 & 17.3 Neuron processes running through the

CNS form tracts of white matter In the PNS, they form peripheral nerves

Neuron Classification Classification by structure

Unipolar- one short process extends from cell body & divides into peripheral & central processes; most distal portions of peripheral process act as dendrites, the rest, along with central process, act as axons; neurons that conduct impulses to the CNS

Bipolar- 2 processes attached to the cell body; found in receptor apparatus of the eye, ear & olfactory mucosa

Multipolar- many processes extending from cell body; single axon, the rest are dendrites; most CNS neurons & those carrying impulses away from CNS are multipolar

Know figure 17.5

Neuron Classification (continued) Classification by function

Sensory (afferent)- carry impulses from sensory receptors in viscera, skin, skeletal muscles, joints or special sensory organs; cell bodies typically found in ganglia outside CNS; typically unipolar

Motor (efferent)- carry impulses from CNS to viscera, body muscles & glands; cell bodies usually in CNS; usually multipolar

Interneurons (association neurons)- situated between pathways connecting sensory & motor neurons; outside CNS; multipolar

Know figure 17.6

Neuroglia of the CNS

Most common glial cell type

Each forms myelin sheath around more than one axons in CNS

Analogous to Schwann cells of PNS

Structure of a Nerve A nerve is a bundle of nerve fibers (processes) wrapped in connective

tissue Extend to and/or from the CNS and viscera or structures of the body

periphery Nerves carrying both sensory (afferent) & motor (efferent) fibers are

called mixed nerves; all spinal nerves are mixed Nerves that only carry sensory impulses to CNS are called sensory

(afferent) Nerves that carry only motor fibers are called motor (efferent) Each fiber is surrounded by an endoneurium Groups of fibers are surrounded by a perineurium, forming bundles

called fascicles Groups of fascicles are bound by epineurium forming a nerve Blood & lymphatic vessels are also present within the nerve Know figure 17.7

Structure of a Multipolar Neuron

Nerve bundle (PNS)

Exercise 19

Gross Anatomy of the Brain and Cranial Nerves

Introduction Divisions:

Central nervous system (CNS)- brain and spinal cord Peripheral nervous system (PNS)- cranial & spinal

nerves, ganglia, and sensory receptors Sensory portion- nerve fibers that conduct impulses

toward the CNS Motor portion- nerve fibers that conduct impulses away

from the CNS Somatic (voluntary) division- controls skeletal muscles Autonomic (involuntary) division- controls smooth & cardiac

muscles and glands Sympathetic division Parasympathetic division

The Human Brain During embryonic development, the CNS first appears as a

neural tube Neural tube then develops into 3 regions

Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain) Remainder of the neural tube becomes the spinal cord

Those 3 regions become the secondary brain vesicles, which then develop into various adult brain structures

Know figure 19.1

The Human Brain (cont.) Cerebral hemispheres (continued)

Hemispheres share some functions Each is also specialized in some ways Left is usually associated with language (analytical) Right is associated with abstract, conceptual, and spatial

processes (artistic & creative) Those functions are mainly carried out in the outermost grey

matter, called the cerebral cortex Most of the deeper tissue, the white matter, is involved in

carrying impulses to & from the cortex

The Human Brain (cont.) Brain stem

Includes: Cerebral peduncles- connect the pons to the cerebrum Pons- primarily sensory & motor fiber tracts that

connect the brain to lower CNS centers Medulla oblongata- primarily composed of fiber tracts;

houses many vital autonomic centers involved in control of heart rate, respiratory rhythm, and blood pressure, as well as involuntary centers controlling vomiting, swallowing, etc.

The Human Brain (cont.) Cerebral hemispheres

Develop out of the telencephalon of the forebrain Most superior portion of the brain Entire surface consists of gyri that are separated by shallow

grooves called sulci (singular = sulcus) & deeper grooves called fissures

Hemishpheres are divided by the longitudinal fissure Frontal & parietal lobes are separated by the central sulcus Temporal & parietal lobes are separated by the lateral sulcus Occipital & parietal lobes are separated by the parieto-

occipital sulcus Know figures 19.2 (a, b, & c, not d) & 19.3

The Human Brain (cont.) Diencephalon

Sometimes considered the most superior portion of the brain stem

Embryologically part of the forebrain Includes olfactory bulbs & tracts, optic nerves,

the optic chiasma, optic tracts, the pituitary gland, and the mammillary bodies

Know figures 19.4 a & b, 19.5

The Human Brain (cont.)

Cerebellum Projects dorsally from under the occipital lobes

of the cerebrum 2 major hemispheres Outer cortex of grey matter & inner white

matter Know figure 19.6

Meninges of the Brain 3 connective tissue membranes: dura mater (outermost),

arachnoid mater, pia mater (innermost) Dural layers are fused together, except in 3 places where the

innermost layer extends inward to secure brain structures (falx cerebri)

Meningitis- inflammation of the meninges; caused by infection Encephalitis- inflammation of the neural tissue of the brain Know figure 19.7

Cerebrospinal Fluid (CSF) Formed by the choroid plexuses Similar to plasma in composition Cushions the brain Circulates from the 2 lateral ventricles to the 3rd ventricle via

the interventricular foramina, then through the cerebral aqueduct into the 4th ventricle

CSF returns to the blood in the dural sinuses Improper drainage leads to a build-up, which puts pressure on

the brain in adults; causes hydrocephalus in infants Know figure 19.8

Cranial Nerves Actually part of the PNS 12 pairs Primarily serve the head & neck; only the vagus

nerves extend into the thoracic & abdominal cavities

Most are mixed; exceptions are the optic, olfactory & vestibulocochlear

Table 19.1: know name, number & function Know figure 19.9

Human brain

Human brain sagittal

Our brain model

Sheeps brain

Sheep sagittal #1

Sheep sagittal #2Sheep brain 1. cerebrum 2. lateral ventricles 3. third ventricle 4. cerebral aquaduct 5. fourth ventricle 6. pons 7. cerebellum 8. arbor vitae 9. medulla oblongata 10. genu of corpus callosum 11. body of corpus callosum 12. splenium of corpus callosum 13. fornix 14. massa intermedia 15 & 21. optic chiasma 16. hypophysis 17. infundibulum 18. mammillary body 19. superior colliculus 20. olfactory bulbs 21 & 15. optic chiasma 23. longitudinal cerebral fissure 24. cerebral cortex 25. central white matter 26. choroid plexus

Sheep frontal sectionsSheep brain 1. cerebrum 2. lateral ventricles 3. third ventricle 4. cerebral aquaduct 5. fourth ventricle 6. pons 7. cerebellum 8. arbor vitae 9. medulla oblongata 10. genu of corpus callosum 11. body of corpus callosum 12. splenium of corpus callosum 13. fornix 14. massa intermedia 15 & 21. optic chiasma 16. hypophysis 17. infundibulum 18. mammillary body 19. superior colliculus 20. olfactory bulbs 21 & 15. optic chiasma 23. longitudinal cerebral fissure 24. cerebral cortex 25. central white matter 26. choroid plexus

Exercise 20

Electroencephalography

Brain Wave Patterns and the Electroencephalogram EEG- record of the electrical activity of the brain Recorded as waves Represents summed synaptic activity of many

neurons Frequency of 1-30 Hz (cycles per second) Dominant rhythm of 10 Hz Average amplitude of 20-100 microvolts Vary in frequency in different areas of the brain

Brain Wave Patterns (cont.) Waves

Alpha waves- average frequency of 8-13 Hz; produced in a relaxed state with eyes closed; alpha block (suppression) occurs if eyes are opened or if the person begins to concentrate on something; as concentration or excitement increases, frequency increases & amplitude decreases

Beta waves- related to alpha waves, but with higher frequency (14-30 Hz) & lower amplitude; typical of alert state

Brain Wave Patterns (cont.) Waves (cont.)

Delta waves- very high amplitude; frequency of 4 Hz or less; seen in deep sleep

Theta waves- frequency of 4-7 Hz; high amplitude; abnormally contoured; normal in children; abnormal in adults

Brain waves vary with age, sensory stimuli, brain pathology, and chemical state of body

Spontaneous brain waves are ALWAYS present Lack of brain waves is considered clinical

evidence of death

Brain wave patterns

Exercise 21

Spinal Cord, Spinal Nerves, and the Autonomic Nervous System

Anatomy of the Spinal Cord Continuation of the brain stem Association & communication center Enclosed within the vertebral column Extends from the foramen magnum to the 1st or 2nd lumbar

vertebra, terminating in the conus medullaris The filum terminale, an extension of the pia mater, extends

into the coccygeal canal CSF does flow through the spinal canal and can be removed

below L3 (lumar tap) 31 pairs of spinal nerves Know figures 21.1 & 21.2

Grey Matter Looks like an H or a butterfly in the spinal cord The dorsal horns contain interneurons & sensory

fibers The ventral horns mostly contain cell bodies of

motor neurons of the somatic division of the motor portion of the PNS

The lateral horns contain cell bodies of motor neurons of the sympathetic division of the ANS (PNS)

White Matter Composed of myelinated fibers White matter on each side of the spinal cord is divided into 3 white

columns: Posterior funiculi Lateral funiculi Anterior funiculi

Each funiculus contains tracts Ascending tracts carry sensory impulses to the brain Descending tracts carry motor impulses from the brain

Severe trauma to the cord can cause a loss of both sensory & motor functions served by that area of the cord, as well as below Paraplegia- permanent flaccid paralysis of both legs Quadriplegia- permanent flaccid paralysis of all 4 limbs

The Autonomic Nervous System (ANS) Subdivision of PNS Also called involuntary nervous system Regulates body activities not normally under voluntary control Serves cardiac & smooth muscle & internal glands Consists of chains of 2 motor neurons:

Preganglionic neuron- resides in the brain or spinal cord; its axon leaves the CNS & synapses with the 2nd (ganglionic) neuron

Ganglionic neuron- resides in a ganglion outside the CNS; its axon extends to the organ it serves

2 divisions: sympathetic & parasympathetic

ANS Parasympathetic & sympathetic divisions have antagonistic

effects Parasympathetic division

“Resting & digesting” system Maintains internal organs for normal functions & homeostasis

Sympathetic division “Fight or flight” response Readies the body to deal with situations that threaten

homeostasis Increases heart rate & blood pressure, dilates bronchioles in

the lungs, increases blood sugar levels, etc.

Spinal cord

Spinal cord cross section