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– 1st , 2nd and 3rd 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– 11% of total brain mess – Dorsal to the pons and medulla – Two hemispheres connect via the ‘vermis’ – Folia: convoluted surface (“leaves”)– Largest neurons: Purkinje cells (multineurons)– 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 3rd 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, 3rd and 4th

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