Nervous Tissue II

BIO 408

Histology

Dr. D. L. Daley

The Central Nervous System

n Spinal Cord

n Brain

Spinal Cord

n Located within the dorsal vertebral column

n From base of the brain to the pelvis

n In humans the posterior few segments are filled with nerves that supply the pelvis, buttocks & legs

Spinal cord

n Gray matter around a central canal - butterfly shape

n Cell bodies, dendrites & synapses

n White matter surrounds gray matter

n Bundles of myelinated axons that connect different parts of the cord

n Spinal nerves - sensory & motor

n Dorsal root - sensory - dorsal root ganglion (sensory cell bodies)

n Ventral root - motor

Spinal Cord

Ganglia

n Collection of cell bodies of neurons located outside the CNS

n Types

n Sensory - House the cell bodies of sensory neurons

n Autonomic - House the cell bodies of postganglionic autonomic nerves

Sensory Ganglia

n Associated with cranial nerves V, VII, IX and X and each of the spinal nerves originating from the spinal cord

n Dorsal root ganglia - sensory ganglia of the spinal nerves

n Unipolar or pseudounipolar cells - enveloped by capsule cells

n Capsule cells are surrounded by a connective tissue capsule composed of satellite cells

Autonomic Ganglia

n House the cell bodies of postganglionic neurons (motor since they innervate smooth muscle, cardiac muscle or glands

n Sympathetic chain ganglia - adjacent tot he spinal cord

n Collateral ganglia - along the abdominal aorta in the abdomen

n Preganglionic neurons synapse on the postganglionic cell bodies

Brain Architecture

n Front part of the brain increases in size & surface area from fish to mammals

n The surface thrown into folds - gyri (gyrus - singular)

n The grooves between the folds are sulci (sulcus - singular)

Brain Architecture

n Tracts occur on the surface & deeper

n Gray matter - forms distinct collections of cell bodies - nuclei

n Cortex - opposite of spinal cord

n Outside - gray matter with white below (complex tangles of tracts below - with deep nuclei)

Brain

External Coverings

n Meninges - three membranes

n Outermost - dura mater - tough inelastic bag surrounds the brain & spinal cord

n Middle most membrane - arachnoid membrane - appearance & consistency resembling a spider web

n Innermost - pia mater - thin membrane that adheres closely to the surface of the brain

n Pia mater is separated from the arachnoid by fluid filled subarachnoid space

Cerebral Cortex

n The cerebral cortex is organized into 6 layers composed of neurons

n Each layer exhibits a unique morphology

n Most superficial is next to the pia mater

n The sixth or deepest layer is bordered by white matter

Cerebral Cortex

Cells of the Cerebral Cortex

n Pyramid cell - 10mm to 100mm (motor cortex)

n 70% of cells - output cells

n Stellate cells - show diverse morphology, but typically small and multipolar

n Martinotti cells - spinous soma & long ascending axons

n Fusiform cells - in deep layers, spindle shaped with axon entering white matter

Cerebral Cortex

Cerebellum

n Composed of two hemispheres, deeply folded into fissures and lobes

n The outer gray matter - cortex

n Below the cortex is branched cores of white matter

n Embedded deep in the white matter are deep nuclei

Cerebellum

n A central point for motor organization. Yet it does not initiate movement and movement can be generated in the absence of it

n The cerebellum modulates or reorganizes motor commands - and by coordinating diverse signals, it obtains the maximum efficiency from them

Cerebellum

n Lesions - produce disturbances in the coordination of limb and eye movements and disorders of muscle tone and posture

n Principal cell - Purkinje cell - projects to deep cerebellar nuclei

Cerebellar Cortex

n Three layers

n Molecular layer - directly below the pia mater - stellate cells and the dendrites of Purkinje cells and the axons of granule cell (called parallel fibers)

n Purkinje cell layer - large flask shaped cells - dendrites in one plane in the molecular layer - may receive inputs from 200,000 parallel fibers

n Output of Purkinje cells is always inhibitory on deep cerebellar nuclei

n Granule cell layer - small cells - axons ascend into the molecular layer and form the parallel fibers

Purkinje Cells