Nervous System Structure

The Nervous System

• Central Nervous System (CNS)

• Peripheral Nervous System (PNS)

Neuraxis

• The imaginary line drawn through the CNS, from the base of the spinal cord to the front of the brain.

Nervous system directions, in relation to the neuraxis

• Anterior / Rostral– Toward the nose

(rOstral nOse)

• Dorsal– Toward the back

• Superior– Above

• Lateral– Away from the midline

• Ipsilateral– Same side

• Posterior / Caudal– Toward the tail

(cAudal tAil)

• Ventral– Toward the belly

• Inferior– Below

• Medial– Toward the midline

• Contralateral– Opposite side

Contralateral Ipsilateral

Nervous system planes

• Transverse– Cross section

• Sagittal– Sagittal section

• Horizontal– Horizontal section

Layers of the meninges

Brain

Pia mater

Arachnoid trabeculae

Subarachnoid space

Arachnoid membrane

Dura mater

Meninges

• Three protective layers surrounding the brain and spinal cord– Dura Mater– Arachnoid

membrane– Pia mater

Ventricles

• Openings in the brain that contain cerebrospinal fluid (CSF)

Cerebrospinal fluid

• CSF is made in the choroid plexus

• CSF flows through the ventricles into the subarachnoid space, where it surrounds the CNS.

Neural development

• Neural tube– Develops into the CNS

• Neural tube forms 3 ventricles at the rostral end

• Tissue surrounding ventricles = ventricular zone

• Forebrain– Telencephalon– Diencephalon

• Midbrain (Mesencephalon)– Tectum– Tegmentum

• Hindbrain– Metencephalon– Myelencephalon

Neural development

Cellular development

• Founder cells - in developing brain– Initial cells in the ventricular zone– Symmetrical division

• Increases size of the ventricular zone

– Asymmetrical division• Creates neurons while maintaining ventricular

zone

• Stem cells - in the adult brain

Cellular development

• Radial glia

• Radial glia ensure development of systematic pathways in the brain.

Cellular development

• Cortical development ends with apoptosis

• Neurons grow into adult form with dendrites, axons & terminal buttons

• Neurons that do not connect with other neurons die

Forebrain - Telencephalon

• Telencephalon– Cortex– Limbic system– Basal ganglia

Telencephalon

• Cerebral cortex – surrounds the cerebral hemispheres– Gyri (singular: Gyrus) – Sulci (Sulcus)– Fissures

• Cortex consists of densely packed glia and neurons

• Four lobes of the brain– Frontal– Parietal– Temporal– Occipital

Cortex - Frontal lobe

• Prefrontal Cortex– Involved in organization of thought, planning

actions, and higher cognitive functions.

Cortex - Frontal lobe

• Primary motor cortex (PMC)– Directly controls motor

output– Somatotopic organization

• Motor Association Cortex– Involved in planning

movement

Cortex - Parietal lobe

• Primary Somatosensory Cortex– Receives sensory information– Somatotopic organization

• Somatosensory Association Cortex– Somatosensory perception and memories

Cortex - Temporal lobe

• Primary Auditory Cortex– Receives auditory input

• Auditory Association Cortex– Analyzes auditory information– Auditory perception and memory storage

Coretex - Occipital lobe

• Primary Visual Cortex– Receives input from the visual system– Input comes from the contralateral

visual field

• Visual Association Cortex– Analyzes information received in the

PVC– Involved in visual perception

Cortical connections

• Corpus Callosum – large bundle of axons connecting corresponding regions of each hemisphere

Telencephalon – Limbic system

• Limbic system– Located within the telencephalon– Includes:

• Limbic cortex• Amygdala• Hippocampus• Mammillary bodies of the

hypothalamus• Fornix

Limbic system

• Major role in emotion, learning and memory

Telencephalon – Basal ganglia

• Basal ganglia – Motivation and generation

of movement

• Include:– Caudate nucleus– Putamen– Globus pallidus

Forebrain - Diencephalon

• Diencephalon• Located between the

telencephalon and the midbrain

– Includes: • Thalamus• Hypothalamus

Diencephalon

• Thalamus– Composed of nuclei that relay information to

the proper cortical regions– Projection fibers

Diencephalon

• Hypothalamus– Controls the autonomic nervous system

and the endocrine system– Two major structures control endocrine

function• Anterior pituitary gland• Posterior pituitary gland

Midbrain (Mesencephalon)

• Structurally and evolutionarily between the diencepalon and the hindbrain

• Only two major structures– Tectum– Tegmentum

Midbrain - Tectum

• Located on the dorsal mesencephalon– Superior colliculi – Inferior colliculi

Midbrain - Tegmentum

• Located on the ventral mesencephalon– Reticular formation – Periaqueductal grey area – Red nucleus – Substantia nigra

Hindbrain

• Most primitive brain structure; responsible for basic survival functions

• Consists of the metencephalon and myelencephalon

Hindbrain - Metencephalon

• Cerebellum (dorsal brainstem)– Attached to the pons by the cerebellar

peduncles– Coordinates movement

• Pons (ventral brainstem)– Projects information from cortex to

cerebellum– Role in sleep and arousal

Hindbrain - Myelencephalon

• Caudal-most region of the brain– Contains the medulla oblongata

• Cardiovascular & respiratory functions, muscle tone, arousal

Spinal cord

• Cells of the spinal cord– Grey matter

• Cell bodies and unmyelinated axons• Dorsal horns• Ventral horns

– White matter• Myelinated axons

web.lemoyne.edu/.../graphics/spinal_cord.jpg

Spinal cord

• Spinal nerves– 31 pairs of spinal nerves attach to the spinal

cord– Each spinal nerve consists of a motor efferent

(output) and a sensory afferent (input)– As each nerve approaches the spinal cord, it

splits into a dorsal and ventral root

Spinal cord

• Dorsal root – carries the sensory axon– Cell body is in the dorsal root ganglion – Axon enters the spinal cord

• Ventral root – carries the motor axon– Cell body is in the ventral

horn of the spinal cord– Axon exits to the periphery

Cranial nerves

• 12 pairs of cranial nerves attach to the ventral surface of the brain.– Sensory & motor functions of the face,

head, neck and throat.

Peripheral Nervous System

Somatic Nervous System Autonomic Nervous System

Parasympathetic Nervous System

Sympathetic Nervous System

“Fight or Flight” Response

Utilization of energy resources

“Rest & Digest” Response

Conservation of energy resources

Sensory input

Motor control