Spinal Cord and Cranial Nerves PDF

The Central Nervous System Spinal Cord & Cranial Nerves Learning Outcomes You will be expected to know the following with regard to the spinal cord Location Function Gross anatomy Internal structure Protections Number of spinal nerves Awareness of related...

The Central Nervous System Spinal Cord & Cranial Nerves Learning Outcomes You will be expected to know the following with regard to the spinal cord Location Function Gross anatomy Internal structure Protections Number of spinal nerves Awareness of related pathologies  Function Nervous tissue link for nerve impulses travelling to and from the brain Spinal nerves leave/enter the cord at the appropriate level and pass to the structures they supply (motor and sensory impulses) The major reflex centre and conduction pathway Processes reflex responses in response to environmental changes Independent of the brain Location The spinal cord & spinal nerve are located within the vertebral canal Continuous with the medulla oblongata superiorly extends from the foramen magnum to lower border of L1 (variable) Anchored by the filum terminale, to the coccyx Gross Anatomy Cylindrical in shape Slightly flattened from anterior to posterior It is a tube neural tube Medulla oblongata to L2 42 – 45 cm long ¾” diameter ( about the size of your little finger Tapers to form the medullary cone at L1/L2 Gross Anatomy Cauda Equina (horses tail) Loose bundle of spinal nerve roots arising from the lumbar enlargement and medullary cone Terminal filum Arises from the tip of the medullary cone; attaches to the dorsum of the coccyx. It is an anchor for the inferior part of the spinal cord and meninges Gross Anatomy Internal Structure The cord is enlarged in 2 regions in relationship to innervation of the limbs Cervical enlargement Extends from C4 through to the T1 segment of the spinal cord Most of the anterior rami arising from it form the brachial plexus Lumbosacral enlargement Extends from T11 through to S1 Anterior rami arising from this enlargement make up the lumbar and sacral plexuses that innervate the lower limbs Internal Structure Divided into 2 equal parts by: Anterior median fissure Posterior median fissure Composed of grey matter in the centre, surrounded by white matter. (opposite to the brain)  Grey Matter Central area of grey matter is H or butterfly shaped 2 posterior, 2 anterior, 2 lateral columns (one each side of the midline) Centre of this commisure is the central canal containing CSF (which is continuous with the 4th ventricle above) Consists primarily of nerve cell bodies: Sensory (receives impulses from body) Motor (transmit impulses to muscle) Connector (reflex arc)  White Matter Arranged into 3 columns anterior, posterior, lateral Ascending tracts – sensory axons that conduct impulses to the brain Descending tracts – motor axons carrying nerve impulses down the cord from the brain Spinal cord Protection Bony Vertebrae (contained within vertebral canal) Surrounded by: Cushion of CFS Spinal meninges (similar to the brain) 1. Dura mater 2. Arachnoid mater 3. Pia mater Easy way to remember order of the meninges (inner to outer) “the meninges PAD the brain” Pia; Arachnoid; Dura Dura Mater Outermost covering membrane Tough layer of fibrous and elastic tissue Forms the spinal dural sac (only 1 layer – brain has 2)  Arachnoid Mater Middle covering Delicate, avascular membrane Ensheaths spinal cord and nerve roots Connected to pia mater by arachnoid trabelculae Lines the dural sac  Pia Mater Innermost covering Thin transparent layer of connective tissue closely follows the contours of the spinal cord Covers spinal nerve roots Contains small blood vessels that nourish the cord Level of L2, the pia mater extends as the filum terminale to attach on to the coccyx  Pia Mater The spinal cord is suspended within the dural sac by 21 pairs of Denticulate ligaments thickenings of pia mate that extend laterally, fuse with arachnoid mater and secure the cord in place  Epidural Space Between the bony wall of the vertebrae and the dura mater Contains cushioning of fat, blood vessels and connective tissue Runs from the length of the vertebral canal (NB there is NO epidural space around the brain) Subarachnoid Space Between the arachnoid and the pia mater Spanned by arachnoid trabelculae Filled with Cerebrospinal fluid (CSF) sagittal view of cord in situ 1. Intervertebral disc 2. Vertebral body 3. Dura mater 4. Epidural space 5. Spinal cord 6. Subarachnoid space  Spinal Nerves Peripheral Nervous System (PNS) = spinal nerves and cranial nerves 31 pairs of spinal nerves Arise from both sides of the spinal cord Emerge through the intervertebral foramina Names/grouped according to associated vertebrae  Spinal Nerves Cervical x 8 First spinal nerve emerges between C1 and occipital bone Thoracic x12 Lumbar x5 Cauda equina = sheaf of nerves Sacral x5 Coccygeal x1  Nerve Roots Each nerve is formed by the union of an anterior (motor) and posterior (sensory) nerve root, and is therefore a MIXED nerve (when leaving the spinal cord the nerve roots are covered in dura and arachnoid – these terminate when they join) Spinal cord Spinal Nerves Cranial Nerves Learning Outcomes By the end of this session you should be able to:- Identify the 12 cranial nerves by Name Number Type Function Peripheral Nervous System PNS consists of:- 1. Sensory neurons (Sometimes called afferent neurons) Carrying impulses from receptors in the ‘periphery’ to the CNS 2. Motor neurons (sometimes called efferent neurons) Carrying impulses from the CNS to muscles and glands Peripheral Nervous System PNS can be subdivided into:- Somatic Nervous System (voluntary) 12 pairs of cranial nerves – sensory, motor or mixed 31 pairs of spinal nerves – mixed Ganglia (groups of nerve cell bodies) Autonomic Nervous System (involuntary) Viscera (organs) of the body are supplied by fibres from two divisions Sympathetic division – increases organ activity Para-sympathehtic division – decreases organ activity Cranial Nerves Peripheral Nervous System 12 pairs Each has both a number (in roman numerals) and a name numbered from superior to inferior, from which they arise Name designates its distribution or function 10 originate from the brain stem 2 (CNI and CNII) are extensions of the forebrain Some are purely sensory, some motor and some are mixed All emerge through the foramina or fissures in the cranium  Cranial Nerves (12) I. Olfactory VII. Facial II. Optic VIII. Vestibulocochlear III. Oculomotor IX. Glossopharangeal IV. Trochlear X. Vagus V. Trigeminal XI. Accessory VI. Abducens XII. Hypoglossal On On On They Travelled And Found Voldemort Guarding Very Ancient Horcruxes  CNI. Olfactory Nerve (S) Nerve of the sense of smell Olfactory nerve fibres pass from the nasal cavity through the cribiform plate to synapse with the olfactory bulb The olfactory tracts the then proceeds to the temporal lobe, the area of perception of smell (also involves the limbic system) Lesions of the nerve result in parosmia ( altered sense of smell) or anosmia (loss of smell) Function test – smelling common objects  Nerve of sense of sight Sensory nerve cells arise from the retina and CNII Optic Nerve (S) converge at the posterior eye to form the optic nerve Passes through the optic canal The optic nerves join at the optic chiasm anterior to pituitary stalk, where the fibres from the medial side of the retina cross to the opposite side –allows binocular vision The optic nerves terminate in the thalmus, but optic radiations continue to the visual cortex Function test – charts for acuity, visual field, colour Lesions of the visual pathway result in blindness and pupillary abnormalities CNIII Oculomotor (M) Movement of the eyeball (elevation, adduction) superior, inferior, medial rectus muscle Focusing; regulating pupil size Ciliary muscles; circular muscles CN IV Trochlear (M) Movement of the eyeball (depression) Superior oblique muscles  CNV Trigeminal Nerves (mixed) Largest of the cranial nerves Primarily involve in sensation in the face, but also chewing, biting & swallowing (mastication) Three main branches Opthalmic – sensory Maxillary – sensory Mandibular - mixed CN VI Abducent (M) Movement of the eyeball (abduction) lateral rectus muscle CN VII Facial (Mixed) Facial Expression; Sense of Taste sensory fibre to tongue motor fibre to face  CN VIII Vestibulocochlear (S) Passes through the internal auditory canal Has 2 sets of fibres: Vestibular branch – impulses from the semi-circular canals to areas of the cerebellum that aid balance and posture Cochlear branch – impulses from the inner ear to the areas in cerebral cortex that interpret sound Function tests – tuning fork(hearing); closing eyes (balance)  CN IX Glossopharangeal (mixed) Taste; secretion of salvia; movement of the Pharynx Parotid Gland Back of tongue CN X Vagus (mixed) Distributed in the head, neck, thorax and abdomen Taste; talking & swallowing; secretion Sensory – taste & sensations from throat; BP & O2 monitoring; regulates breathing; visceral sensations from organs in thorax and abdomen Motor – swallowing; coughing; voice production (parasympathetic) – smooth muscles of GI tract; slowing of heart rate; digestive sections CN XI Accessory (M) Cranial & spinal root (originates from both brain and spinal cord) Swallowing (cr); Movement of head and shoulders (SC) Pharynx & larynx Sternocleidomastoid & trapezius muscles CN XII Hypoglossal (M) Tongue movement Base Of Skull A. Optic canal B. Foramen rotundum C. Foramen ovale D. Foramen spinosum E. Foramen magnum F. Hypoglossal canal G. Jugular foramen H. Internal Acoustic Meatus(IAM) I. Foramen lacerum J. Cribriform plate P234, Bones and Joints – review the foramen through which each CN nerve passes