A Journey Through the Central Nervous System

Stimulus travels towards the spinal cord – Via somatic sensory neuron Dorsal root ganglion – Collection of sensory nerve nuclei Anterior horns of gray – Synapse with interneurons

17 inches long and ¾ inch thick Bone and epidural space – Fat and veins Spinal dura mater – Subdural space and arachnoid mater Subarachnoid space – Between arachnoid and pia mater – CSF

A sagittal view of the human thoracic spinal cord, showing the (1) intervertebral discs, (2) vertebral bodies (3) dura mater (4) epidural space (5) spinal cord (6) subdural space. bodies.

Lumbar Tap

Terminates at the conus medullaris – Ends at L1 – L2 Filum Terminale – Extension of conus (covered by pia mater) – anchors spinal cord to coccyx – Denticulate ligaments (saw-tooth like pia mater) attach to dura mater Spinal Nerves – 31 pairs move out through intervertebral formaina Cauda Equina – Nerve roots exit terminal end of spinal cord

Composed of myelinated and unmyelinated nerve fibers Run in three directions – 1. ascending (sensory inputs) – 2. decending (motor inputs) – 3. Transversely (side to side in spinal cord) Our sensory input moves toward the brain – Ascending fiber tracts

The ascending tracts are called: – 1. Dorsal White Columns Skin (touch, pressure, limb and joint position, upper limbs and trunk, neck) – 2. Anterior/posterior spinalcerebellar tracts Trunk and lower limb impulses to cerebellum – 3. Anterior spinothalamic tract Touch and pressure to somatosensory cortex – 4. Lateral spinothalamic tract Pain and temperature info to the somatosensory cortex Several neuron chains synapse in the ascending tracts – 1 st, 2 nd and 3 rd order neurons

Anterolateral Pathways - lateral and anterior – Lateral and anterior spinothalamic tracts – Older pathway

Relays precise transmissions of inputs from a single type of sensory receptor (touch and vibration) Includes – Dorsal white column – Medial lemniscal tracts Terminates in the thalamus – continues onto the somatosensory cortex

Muscle tendon stretch to cerebellum Coordinates skeletal muscle activity – No conscious sensation

Trauma – Paralysis and Flaccid Paralysis – Spastic paralysis – Quadriplegia Disorders – Polio – Amyotropic Lateral Sclerosis

Processes inputs from: – Cerebral motor cortex – Bran stem nuclei – Sensory receptors (via spinocerebellar tracts) Functions – Precise timing and patterning skeletal muscle contractions – Smooth and coordinated movements – Agility

Anatomy –1–11% of total brain mess –D–Dorsal to the pons and medulla –T–Two hemispheres connect via the ‘vermis’ –F–Folia: convoluted surface (“leaves”) –L–Largest neurons: Purkinje cells (multineurons) –W–White matter: arbor vitae (“tree of life”)

Fiber tracts connect the cerebellum to the brain stem – 1. Superior peduncles: midbrain and cerebellum Neurons inside cerebellum to motor cortex (via thalamus) – 2. Middle peduncles: one-way, pons to cerebellum Pons notifies the cerebellum of voluntary motor activity initiated by voluntary motor cortex – 3. Inferior peduncles: medulla and cerebellum Sensory information to cerebellum from muscles in the body and vestibular nuclei of brain stem (balance and equilibrium)

Pathways- enter the medulla oblongata at the base of the spinal cord Both specific and nonspecific tracts Olives – Contain nuclei that relay state of stretch of muscles and joints to cerebellum Nucleus gracilis and cuneatus – Associated with specific ascending pathway

Location – Between the medulla and midbrain Anatomy – Composed of conduction tracts Deep projection tracts connects higher brain centers and spinal cord

Location – Between diencephalon and pons Functions and Anatomy - nuclei – Corpora Quadrigemina Superior colliculi – coordinate visual reflexes like head and eye movements Inferior colliculi – auditory relay ear to sensory cortex of cerebrum – Peduncles (associated with motor tracts)

1. Hypothalamus 2. Thalamus 3. Epithalamus

Location – Superior to brain stem – Makes walls of 3 rd ventricle Function and Anatomy – Mammillary bodies – Infundibulum and Pituitary gland – Other functions (page 446)

Location – Superior to the hypothalamus Function and Anatomy – Connected by intermediate mass – All ascending tracts move through the thalamus to the cerebral cortex through nuclei – Many nuclei Ventral posterior lateral nucleus – Impulses from general somatic sensory receptors for touch, pressure, pain) Geniculate bodies – Visual and auditory relay centers

As the fibers move up to the higher brain centers: – Form Projection tracts – Corona Radiata (radiating crown) Tracts pass through internal capsule Radiate out and eventually reach the cerebral cortex

2 Cerebral Hemispheres (83% of total brain mass) – Lobes and fissures – White matter and Gray Matter (Cerebral Cortex) Giri and Sulci Cerebral Cortex – The conscious mind – Composed of sensory areas 1. Primary somatosensory cortex 2. Somatosensory association cortex 3. Primary visual cortex (striate) 4. Primary auditory cortex 5. Olfactory cortex 6. Gustatory cortex 7. Visceral sensory area 8. Vestibular cortex

1. Visual 2. Auditory 3. Multimodal Association Areas – (a). Anterior – (b). Posterior – (c). Limbic

1. Primary (somatic) motor cortex – Pyramidal cells and corticspinal tracts 2. Premotor cortex – Skilled motor activities – Planning movements 3. Broca’s area – Left hemisphere only – Motor speech area 4. Frontal Eye Field – Voluntary movement of the eye

1. Pyramidal (Direct) Tracts – Lateral and corticospinal tracts 2. Extrapyramidal Pathways – Tectospinal Motor impulses from midbrain – coordinated movment of head and eyes – Vestibulospinal Motor impulses for muscle tone; activates limb and trunk extensor muscles that move head; balance (standing and moving) – Rubrospinal Muscle tone of distal limbs – Reticulospinal Muscle tones; visceral motor functions; unskilled movements

Hypothalamus- Visceral Control Center (page 446) Midbrain – Cerebral peduncles Corticospinal tracts – Cerebellar peduncles Connect midbrain to cerebellum – Red nucleus Relays motor pathways for limb flexion Pons – Middle cerebellar peduncles Connect cerebral cortex to cerebellum

Corticospinal Tracts cross-over – Decussation (a “crossing”) of the pyramids Control – 1. Cardiovascular center – 2. Respiratory centers – 3. Vomiting, hiccuping, coughing, sneezing

Enter the ventral and anterior horns of gray and lateral horns of gray Exit anterior horn Enter the spinal nerves On to the effector organs – Somatic (skeletal muscles) – Visceral (visceral organs)

Ventricles Openings in the cerebrum which contains Cerebral Spinal Fluid. Will circulate in parts of the brain and eventually spinal cord Lateral, 3 rd and 4 th Subarachnoid space (page 466)

In cerebral white matter Nuclei – 1. Putamen and globus pallidus (lentiform nucleus) – 2. Caudate nucleus and lentiform nucleus Corpus striatum Input from cerebral cortex and other nuclei Influence muscle movement Other functions – Starting, stopping, slow or stereotyped movement – Nuclei associated with substantia nigra of midbrain Dopamine releasing neurons degenerate – Parkinson’s