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Lecture # 21: The Brain and Cranial Nerves

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1 Lecture # 21: The Brain and Cranial Nerves
(Chapter 14) Objectives: 1- Name the major regions of the brain and give the functions of each. 2- Name the three coverings of the central nervous system and give the characteristics, location, and function of each. 3- Give the functions of cerebrospinal fluid and explain its formation, circulation, and resorption.

2 Major Landmarks of the Brain
I-Cerebrum II- Brain Stem III- Cerebellum Foramen magnum Spinal cord

3 Major Landmarks of the Brain
II- Brain Stem BRAIN 1- Diencephalon I- Cerebrum a-Thalamus b- Hypothalamus C- Epithalamus 2- Midbrain d- Cerebral peduncles a c e- Corpora quadrigemina b e d 3- Pons III- Cerebellum 4- Medulla oblongata Foramen magnum Spinal cord

4 I- The Cerebrum Frontal lobe Frontal lobe Parietal lobe Insula
Right hemisphere Left hemisphere Central sulcus Precentral gyrus Postcentral gyrus Gyrus Gyri Frontal lobe Frontal lobe Precentral gyrus Parietal lobe Central sulcus Insula Postcentral gyrus Lateral sulcus Temporal lobe Occipital lobe Parietal lobe Occipital lobe Longitudinal fissure It separates the right and left hemispheres

5 Cranial Meninges Skull Dura mater: Arachnoid mater Pia mater
Arachnoid villus Dura mater: Periosteal layer Superior sagittal sinus (contains blood) Meningeal layer Arachnoid mater Subarachnoid Space (contains CSF) Pia mater Falx cerebri (in longitudinal fissure only)

6 Ventricles and Cerebrospinal Fluid
Lateral ventricles Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle Central canal

7 Interventricular foramina (foramina of Monro)
Septum pelucidum It separates the lateral ventricles Interventricular foramina (foramina of Monro) They communicate the lateral ventricles with the third ventricle Cerebral aqueduct It communicates the third ventricles with the fourth ventricle They connect the fourth ventricle with the sub- arachnoid space Lateral apertures Medial aperture Central canal

8 The Flow of Cerebrospinal Fluid
CSF is secreted by choroid plexus in each lateral ventricle. CSF flows through Interventricular foramina into third ventricle. Choroid plexus in third ventricle adds more CSF. CSF flows down cerebral aqueduct to fourth ventricle. Choroid plexus in fourth ventricle adds more CSF. CSF flows out two lateral apertures and one median aperture. CSF fills subarachnoid space and bathes external surfaces of brain and spinal cord. At arachnoid villi, CSF is reabsorbed into venous blood of dural venous sinuses.

9 Functional regions of the Cerebral Cortex
It contains the primary somatosensory cortex for touch, pain and temperature. Primary motor cortex Primary somesthetic cortex The neurons send signals for precise, finely coordinated limb movements (contralateral) It interprets the sensory information to making cognitive sense of it Motor association area Somesthetic association area It is where neurons plan a program for the contraction of muscles required for an action such as dancing, typing or speaking Wernicke area It is responsible for the recognition of spoken and written language Visual association area Broca area It generates a motor program for all the muscles of speech It recognizes faces and other familiar objects Primary visual cortex Prefrontal cortex It receives visual signals It gives us a sense of our relationship to the rest of the world, enabling us to think about it and to plan and execute appropriate behavior. Primary auditory cortex Primary gustatory cortex It receives auditory signals Auditory association area It receives gustatory (taste) signals It recognizes the signals received as spoken words, a familiar piece of music, a voice, etc.

10 II- The Brain Stem 1- Diencephalon Thalamus Epithalamus Hypothalamus
It contains the pineal gland that helps regulate the sleep-wake cycle 1- It is the “gateway to the cerebral cortex” – nearly all sensory input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex 2- It is involved in emotional functions Hypothalamus 1- Hormone secretion. It controls anterior pituitary gland. Median section 2- It is the major integrating center for the autonomic nervous system 3- Thermoregulation 4- Hunger center 5- Thirst center that monitors osmolarity of the blood

11 II- The Brain Stem 2- Midbrain Corpora quadrigemina:
Cerebral peduncles Corpora quadrigemina Corpora quadrigemina: Superior culliculi They mediate visual attention and visually tracking moving objects. Inferior culliculi Cerebral peduncles They mediates the reflexive turning of the head in response to a sound They contain the substantia nigra, a motor center that relays inhibitory signals preventing unwanted movements. Median section Degeneration of the neurons of the substantia nigra leads to the muscle tremor of Parkinson’s disease.

12 II- The Brain Stem 3- Pons 4- Medulla oblongata Pons Medulla oblongata
It connects the two hemispheres of the cerebellum Medulla oblongata Median section It contains: 1- Cardiac center (regulates the rate and force of heartbeat) 2- Vasomotor center (regulates blood pressure) 3- Respiratory centers (regulates the rhythm and depth of breathing) Posterolateral view

13 III- The Cerebellum Functions:
1- It monitors muscle contractions and coordinates postural muscles 2- It aids in motor coordination to produce smooth movements

14 Cranial and Spinal Nerves
Cranial Nerves Cervical plexus 1- Olfactory nerve (I) 2- Optic nerve (II) Brachial plexus 3- Oculomotor nerve (III) Thoracic nerves 4- Trochlear nerve (IV) 5- Trigeminal nerve (V) 6- Abducens nerve (VI) 7- Facial nerve (VII) 8- Vestibulocochlear nerve (VIII) Lumbar plexus 9- Glossopharyngeal nerve (IX) 10- Vagus nerve (X) Sacral plexus 11- Accessory nerve (XI) 12- Hypoglossal nerve (XII) Coocygeal plexus

15 Extrinsic muscles of eyes Tongue Head
Three are sensory nerves: Olfactory nerve (smell), optic nerve (vision), and vestibulocochlear nerve (hearing and equilibrium) Four are mixed nerves: Trigeminal nerve, facial nerve, glossopharyngeal nerve, and vagus nerve. Five are motor nerves: Oculomotor nerve, trochlear nerve, abducens nerve, hypoglossal nerve, and accessory nerve. Extrinsic muscles of eyes Tongue Head Olfactory bulb Optic chiasm Olfactory tract Optic nerve (II) Sensory. It provides for the sense of vision. Motor. It innervates four of the six extraocular muscles that move the eyes, the muscle that open the eyelid, the muscle that constricts the pupil, and the muscle that changes the shape of the lens for accommodation. Oculomotor nerve (III) Motor. It innervates the superior oblique muscle of the eye. Trochlear nerve (IV) Mixed. It provides sensory innervation to the face, and motor innervation to the muscles of mastication. Trigeminal nerve (V) Motor. It innervates the lateral rectus muscle of the eye. Abducens nerve (VI) Mixed. It provides motor innervation to the muscles of facial expression, and sensory innervation to taste to the anterior two thirds of tongue. Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Sensory. It provides for the senses of hearing and equilibrium. Vagus nerve (X) Hypoglossal nerve (XII) Mixed. It provides motor innervation to the muscles of pharynx, and sensory for taste to the posterior third of the tongue. Accessory nerve (XI) Mixed. It provides sensory fibers to skin of head and to the pharynx. It provides motor fibers to muscles of speech and swallowing. It innervates most of thoracic and abdominal viscera (parasympathetic nervous system). Motor. It innervates the muscles that move the tongue. Motor. It innervates the muscles that move the head and neck (trapezius, sternocleidomastoid). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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