Central Nervous System Spinal Nerves And Cranial Nerves

Central Nervous System, Spinal Nerves, And Cranial Nerves 10 Unit 1 Chapter 10

Spinal Cord Structure Protection and Coverings 10 • Spinal cord in vertebral cavity. Surrounded by bone • Wrapped in meninges • Spinal cord meninges are continuous with brain meninges Unit 1 3 layers of connective tissue

Spinal Meninges 10 • Epidural space lined with fat • Dura mater- tough , dense connective tissue Extends to 2 nd sacral vertebra Well beyond spinal cord • Arachnoid mater- collagen and elastic fibers • Subarachnoid space • Pia mater- transparent layer adheres to surface of brain & spinal cord Contains blood vessels Unit 1 cerebral spinal fluid circulates in this space

Figure 10. 1

• runs to 2 nd lumbar vertebra • Roots of spinal nerves for lumbar, sacral & coccygeal nerves in vertebral cavity before leaving = Cauda Equina • Enlargements: cervical & lumbar Include nerves for upper & lower limbs • Each spinal segment gives rise to a spinal nerve – 31 pairs 10 Unit 1 Gross Anatomy Of Spinal Cord

Figure 10. 2

Internal Structure Of Spinal Cord 10 • Two grooves- left & right halves Anterior median fissure & posterior median sulcus • Gray matter- 3 horns on each side • Anterior- somatic motor neurons • Posterior- sensory neurons • Lateral- autonomic motor Unit 1 Anterior, posterior, lateral

Internal Structure Of Spinal Cord (cont) 10 • White matter- organized into columns Anterior, posterior & lateral white columns Carry information toward brain • Motor = descending tracts Carry information down spinal cord Unit 1 • Each column contains one or more tracts having a common destination • Sensory = ascending tracts

Figure 10. 3

Spinal Nerves 10 Contains Cell bodies of sensory neurons • Ventral root- axons of somatic & autonomic motor neurons Unit 1 • Serve particular area of body • Contain 2 bundles of axons = roots • Dorsal root- only sensory axons • Swelling called dorsal root ganglion

• Named and numbered according to level of vertebra they emerge from • C 1 -8, T 1 -12, L 1 -5, S 1 -5 & 1 coccygeal • C 1 from above atlas • Rest through intervertebral foramina 10 Unit 1 Spinal Nerves (cont)

• Roots unite to form nerve at foramina • Mixed sensory & motor axons • Each axon wrapped in endoneurium • Axons grouped in fascicles wrapped in perineurium • Outer covering = epineurium 10 Unit 1 Spinal Nerve Composition

Figure 10. 4

• After leaving vertebra nerves branch • Some join with axons from neighboring nerves to form plexuses • Names then relate to area they are in or region innervated • Spinal nerves T 2 -T 11 do not form plexuses= intercostal nerves Supply abdominal muscles, skin of chest & back and muscles between robs. 10 Unit 1 Distribution Of Spinal Nerves

Plexuses 10 e. g. ilioinguinal, femoral, obdurator nerves • Sacral plexus- buttocks, perineum & lower limbs e. g. Gluteal, sciatic & pudendal nerves Unit 1 • Cervical plexus- posterior head, neck, shoulders & diaphragm • Brachial plexus-upper limbs & some neck & shoulder muscles • Lumbar plexus- abdominal wall, external genitals & part of lower limbs

Figure 10. 2

• Routes signals along pathways • Gray matter integrates signals • Reflex = fast involuntary sequence of actions in response to a stimulus • Inborn reflex e. g. withdrawal reflex • Can also have learned reflexes, e. g. driving skills • Can be spinal or cranial integration 10 Unit 1 Spinal Cord Functions

Reflex arc (patellar reflex) 10 1. Sensory receptor- responds to stimulus Tap below patella 2. Sensory neuron- to dorsal horn & brain 3. Integrating center- e. g. single synapse 4. Motor neuron- from center to effector Via ventral horn 5. Effector- responder (muscle or gland) Patellar reflex- rectus femoris contracts Unit 1 Sensory to motor neurons

Figure 10. 5

Brain-major parts 10 • Brain stem- continuous with spinal cord Medulla oblongata, pons, midbrain • Diencephalon- above brain stem Thalamus, hypothalamus & pineal gland • Cerebrum- at top and largest part • Cerebellum- back of brain stem Means “little brain” • Cranial meninges- dura mater, arachnoid mater & pia mater Unit 1 Surface covered with gray matter- cortex Beneath is cerebral white matter

Figure 10. 6 a

Figure 10. 6 b

Brain blood supply 10 • Requires ~20% body’s oxygen supply 4 min lack => permanent damage Allows lipid soluble materials: O 2, CO 2, alcohol, anesthetic agents but controls entry of other materials • Created by tight capillaries and glial cells Unit 1 • Requires continuous glucose supply • Protected by Blood-brain barrier

Cerebral Spinal Fluid (CSF) 10 • Circulates through ventricles of brain and the subarachnoid space. • 4 ventricles: 2 lateral, third & fourth • Formed in choroid plexuses • Flows through ventricles then from 4 th to central canal of spinal cord & subarachnoid cells Reabsorbed through arachnoid villi into superior saggital sinus Unit 1 = Specialized capillary networks in wall of ventricles covered by ependymal cells

Figure 10. 7

Brain Stem- Medulla 10 • Medulla Oblongata- inferior part of brainstem white matter extending between spinal cord & other parts of brain • several nuclei: cardiovascular center • Medullary rhythmicity area (respiratory rhythm) • Other sensory & reflex motor areas Some related to cranial nerves Unit 1 (heart rate)

Brain Stem- Pons 10 • Pons (bridge)- nuclei & tracts • Ascending & descending tracts • Nuclei – motor relays from cerebrum to cerebellum , respiration & cranial nerves V, VII, VIII Unit 1 Connect left & right of cerebellum

Figure 10. 8

Brain Stem- Midbrain 10 • Connects pons to Diencephalon • Nuclei = substantia nigra, red nuclei, cranial nerves III & IV • Superior colliculi – nuclei involved in tracking visual stimuli • Inferior colliculi – auditory input & startle reflex Unit 1 Large tracts = cerebral peduncles (motor)

• Netlike arrangement of gray and white mater • Ascending part = Reticular Activating System (RAS) • Projects to cerebral cortex & helps maintain consciousness • Inactivation => sleep 10 Unit 1 Reticular formation

Figure 10. 9

Diencephalon 10 • Thalamus- critical relay for sensory input Transmits motor information from cerebellum & basal nuclei to cerebrum Control of ANS-regulation of many activities Control of pituitary and hormone production Regulation of emotional & behavior patterns Regulation of eating & drinking Control of body temperature Regulation of circadian rhythms & states of consciousness Unit 1 • Hypothalamus- important for homeostasis

Figure 10. 10

Cerebellum 10 • Two cerebellar hemispheres • Cerebellar cortex –gray matter • Tree like white matter & nuclei • Attached to brain stem via cerebellar peduncles Unit 1 Posterior to medulla and pons, below cerebrum

• Gets wide range of sensory input • Compares with programmed motor activity from cerebral cortex • Smoothes & coordinates complex activities • Regulates posture & balance • Required for skilled motor activities 10 Unit 1 Cerebellar function

• Cerebral cortex • Internal white mater • Deep gray nuclei • Surface folds = gyri • Grooves between = sulci • Longitudinal Fissure- divides it into left & right hemispheres • Connected by corpus collosum 10 Unit 1 Cerebrum- Structure

Cerebrum- Structure (cont) 10 • Each hemisphere has 4 lobes Frontal, parietal, temporal, occipital Precentral gyrus anterior to sulcus= primary motor area Postcentral gyrus = primary sensory area • Deep gray = basal nuclei (basal ganglia) Globus palladus, putamen, caudate nucleus Unit 1 • Central sulcus separates frontal & parietal

Figure 10. 11 a

Figure 10. 11 b

• Ring of structures on inner border of cerebrum and floor of diencephalon • “emotional brain” – pain , pleasure, anger, affection, docility • Involuntary activity related to survival • Important in memory development 10 Unit 1 Limbic System

Figure 10. 12

• Specialized areas anatomically located • Sensory areas receive input and responsible for perception • Motor areas- initiate movements • Associative areas- complex integration: e. g. memory, emotion, reasoning, etc. 10 Unit 1 Function areas of Cortex

Sensory Areas 10 • Primary somatosensory areapostcentral gyrus. • Primary visual area- occipital lobe • Primary auditory area- temporal lobe • Primary gustatory area – base of postcentral gyrus • Primary olfactory area- medial aspect of temporal lobe Unit 1 input includes: touch, proprioception, pain, itching, tickle, temperature

Motor Areas 10 interacts with premotor area & primary motor area to regulate breathing and speech muscles Unit 1 • Mainly from anterior part of hemisphere • Primary motor area- precentral gyrus • Broca’s speech area-

Association Areas 10 Posterior to primary somatosensory area Integrates sensation- exact shape & texture of object compares with stored memories • Wernike’s area- left temporal & parietal lobes Interprets meaning of speech Right hemisphere adds emotional content Unit 1 • Adjacent to sensory & motor areas • connected with tracts- interpret information • E. g. somatosensory association area

Figure 10. 13

Sensory Pathways 10 Fine touch- body location, texture, size Proprioception- position & motion of body parts Vibratory sensations- fluctuating touch stimuli Unit 1 • Relay information from periphery to cerebral cortex • 3 neurons in each pathway. • Posterior column- medial lemniscus pathway

Figure 10. 14 a

• Spinothalamic pathways • anterior & lateral spinothalamic tracts • Relay impulses for pain, tickle, itch & thermal sensations. 10 Unit 1 Sensory Pathways (cont)

Somatic Motor Pathways 10 Local interneurons- e. g. reflexes Upper motor neurons- corticospinal tracts Basal ganglia- help with muscle tone Cerebellum- coordination Unit 1 • Signals converge on lower motor neurons • Lower motor neurons stimulate muscles directly • Input comes from:

Figure 10. 15

• Left gets input from & sends output to right side of body and vice versa • Left important for spoken & written language, numerical & scientific skills & reasoning • Right more involved with spatial and pattern recognition and emotional content 10 Unit 1 Lateralization

• Process for storing & retrieving information • Involves structural & functional changes • Involves association areas, parts of limbic system & diencephalon • Skill memory also involves cerebellum & basal ganglia 10 Unit 1 Memory

Cranial Nerves (table 10. 2) • • • I II IV V 10 Olfactory- special sensory optic- special sensory -eye oculomotor-Motor eye trochlear- motor eye trigeminal- Mixed • VI abducens- motor eye • VII facial- mixed sensory to front of tongue & motor to facial expression, lacrimal and some salivary glands Unit 1 sensory around eyes & upper mouth motor to chewing

Cranial Nerves 10 • VIII vestibulocochlear- special senses- ear • IX glossopharyngeal-mixed Sensory for rest of tongue, pharynx & palate, blood pressure Motor to pharyngeal muscles, parotid salivary gland Sensory from pharynx, ear, diaphragm, visceral organs in ventral cavity Motor to palatal & pharyngeal muscles & organs in ventral cavity Unit 1 • X vagus-mixed (major visceral nerve)

Cranial Nerves (Cont. ) 10 Unit 1 • XI Accessory-Motor to voluntary muscles including sternocleidomastoid and trapezius • XII hypoglossal. - motor to tongue

• Rapid growth during first few years • Size of neurons & proliferation of neuroglia • Increases development of dendritic branches & synaptic contacts • Decline in brain mass from early adulthood on 10 Unit 1 Aging