The Nervous System The Divisions of the Nervous

The Nervous System

The Divisions of the Nervous System • The Central Nervous System – Brain – Spinal Cord • The Peripheral Nervous System – Mixed Sensory and Motor Nerves – Sensory Nerves – Motor Nerves – Voluntary Somatic Nerves – Involuntary Autonomic Nerves – Sympathetic Nerves – Parasympathetic Nerves

The Divisions of the Nervous System • Somatic v Autonomic – Somatic: voluntary motor neurons; cell body in CNS with axon connecting to skeletal muscle – Autonomic: (internal body organs) Involuntary motor neuron; two neurons with one cell body in CNS and one in PNS 1. Sympathetic - speeds up heart, constricts vessels 2. Parasympathetic controls body under normal conditions

The Neuron The Basics • The cell body: contains the nucleus and dendrites • The Dendrites: carry impulses to the cell body • The Axons: carry impulses away from the cell body • * The Myelin sheath provides insulation for the axon and speeds impulse conduction from the cell body to the axon terminals (white fiber) • * Lose the Myelin sheath and lose control over skeletal muscle (multiple sclerosis)

The Neuron The Basics • Schwann cell are supporting cells that wrap themselves tightly around the axon forming the myelin sheath • Neurilemma: outer most part of the Schwann cell • Nodes of Ranvier: exposed membrane at regular intervals • Receptor ending: peripheral nerve ending specialized for response to particular types of stimuli • Synapse: * region of communication between the axons of one neuron and the dendrites of another • Acetylcholine: chemical transmitter substance released by nerve endings

The Neuron The Basics • Nerve fiber: axon or dendrite of a neuron • Nerve: bundle of axons outside of the central nervous system • Ganglion: group of nerve -cell bodies in the PNS • Tract: collection of nerve fibers in the CNS having the same origin, termination, and function

Types of Neurons • Sensory Neurons (Afferent) Carry impulses to the CNS • Motor Neurons (Efferent) Carry impulses from the CNS to muscles and glands *instructs muscles to contract • Inter-Neurons Carry impulses from one neuron to another • Mixed Neurons Composed of both sensory and motor fibers (e. g. Cranial nerve V – Trigeminal: clenches jaw/chewing, sensation of forehead, cheeks, and jaw)

Types of Neurons • Myoneural Junction Also known as neuromuscular junction; Axon terminal of a motor neuron, synaptic cleft, and sarcolemma of a muscle cell

The Central Nervous System Protected by: • *Bones: cranium and spinal vertebrae, encase the brain and spinal cord • *Meninges: cover the brain and spinal cord, tough membranes composed of three layers 1. dura mater 2. arachnoid 3. pia mater • *Ventricles: cavities within the skull that act as safety valves to relieve pressure • *Cerebrospinal Fluid: surrounds the brain and spinal cord, transfers impacts over a greater surface area acting as a shock absorber

The Central Nervous System • Encephalon or Interbrain • Sits on top of brain stem • Includes cerebrum, cerebellum, medulla oblongata, pons, and midbrain

The Central Nervous System The Brain • The Cerebrum (largest part) – Frontal Lobe – Personality (logic, emotions, memory, consciousness, etc. ) – * Motor area – * Thought processes • Parietal Lobe – Somatic Sensory area • Temporal Lobe – Speech (Broca’s Area) – Auditory area • Occipital Lobe – Visual area

The Central Nervous System • The Cortex – * Outermost layer of Cerebrum – * Gray matter of the brain – Contains most of the convolutions (folds) of the brain

The Central Nervous System The Brain (cont. ) • Cerebellum – * Balance – * Equilibrium – * Coordination

The Central Nervous System The Brain (cont. ) • Hypothalamus – * Regulates body temp – * Regulates water homeostasis – * Regulates metabolism

The Central Nervous System • Hemispheres – Connected by cerebral nerves to opposite sides of the cerebrum • Right Side – Controls left side of body – Controls speech, calculation, and writing – Main language center • Left Side – Controls right side of body – Controls spatial abilities, simple language, comprehension, nonverbal ideation

The Central Nervous System The Brain (cont. ) • Thalamus – Relay station for sensory impulses passing up to the sensory cortex – Encloses 3 rd ventricle of the brain

The Central Nervous System The Brain-stem (joins spinal cord to brain) • Medulla oblongata: *controls vital body functions – – – Heart rate Blood pressure Breathing Swallowing Vomiting

The Central Nervous System The Brain-stem • Pons – “Bridge” area, mostly fiber tracts – Does have important nuclei involved in controlling breathing

The Central Nervous System The Brain-stem • Midbrain – Anteriorly composed of two bulging fiber tracts which convey ascending and descending impulses – Posteriorly, composed of four bulging nuclei which are reflex centers involved with vision and hearing

The Central Nervous System • Meninges – *Dura mater: double layered membrane, outermost covering, very strong, fused to inner surface of skull (periosteal layer) and covers brain (meningeal layer) – *Arachnoid mater: middle layer, web like • Subarachnoid space: area where cerebrospinal fluid – *Pia mater: innermost layer, very delicate, clings to brain and spinal cord following every fold

The Central Nervous System • Brain matter: – Gray: composed of neuron cell bodies; concentrated in cerebral cortex – White: composed of fiber tracts (bundles of nerve fibers); connects various parts of the brain with each other and the spinal cord

The Central Nervous System • Spinal Cord Matter – Gray matter: • located in center of cord in an Hshape consists of cell bodies and dendrites • Anterior or ventral horns contain motor neurons of the somatic (voluntary) NS • Posterior or dorsal horns contain association neurons, interneurons, and sensory neurons • Sensory nerves that enter the cord via the dorsal root have their cell bodies in the dorsal root ganglion • Motor nerves exit the cord via the ventral root • The dorsal and ventral roots make up the spinal nerve

The Central Nervous System • Spinal Cord Matter – White matter: • surrounds gray matter • Consists of myelinated fiber tracts (axons) that transmit impulses to or from the brain or from one side of the cord to the other • Afferent tracts: Fiber tracts that carry sensory impulses to the brain are sensory tracts • Efferent tracts: Fiber tracts that carry impulses from the brain to skeletal muscle are motor tracts

The Central Nervous System • Spinal Cord – *Is the pathway for messages to get from the body to the brain and vice versa via – *It is the reflex center and allows reflex impulses to bypass the brain and go directly to the motor neurons to protect the body

Peripheral Nervous System • Link between CNS and the rest of the body Consists of all nerves outside of the CNS – Cranial Nerves – Spinal Nerves – Autonomic Nervous System • Sympathetic Nerves • Parasympathetic Nerves • Cranial Nerves

Cranial Nerves • On I - Olfactory Old II - Optic Olympus III - Oculomotor Towering IV - Trochlear Tops V - Trigeminal A VI - Abducens Finn VII - Facial And VIII - Acoustic German IX - Glossalpharyngeal Viewed X - Vagus (abdominal viscera, longest nerve) Some XI – Spinal Accessory Hops XII - Hypoglossal • Cranial Nerve Testing Video

Cranial Nerve Assessment Neurological Examination of the Nervous System • Cranial Nerve I – Olfactory: Test sense of smell with spirits of ammonia • Cranial Nerve II – Optic: Test for visual acuity • • read printed material count fingers at distance distinguish light from dark read eye chart

Cranial Nerve Assessment • Cranial Nerve II and III – Optic and Oculomotor • Inspect size and shape of pupils – pupils equal & round • Test pupillary response to light – pupils constrict when a light is shined into eye – opposite eye should reflexively constrict (consensual reaction) – record normal response as “PERL” - pupils equal and reactive to light

Cranial Nerve Assessment • Cranial Nerve III, IV, VI – Oculomotor, Trochlear, Abducens • Test extraocular movements (EOM) by asking patient to look to the extreme left and then up and down; to the extreme right then up and down with no head movement – movements referred to as the six cardinal directions of gaze - Oculomotor: pupillary reaction, Trochlear: eye movement, Abducens: lateral eye movement

Cranial Nerve Assessment • Cranial Nerve V – Trigeminal • Test motor movement by asking patient to clench teeth while palpating temporal muscle (in front of ear) and masseter muscles (muscles used to raise/lower jaw and assists in mastication or chewing) • Test sensation by touching forehead, cheeks, jaw on each side

Cranial Nerve Assessment • Cranial Nerve VII – Facial • Inspect the face at rest and during conversation, noting symmetry, tics, or abnormal movements • Ask patient to raise the eyebrows, frown, show both upper and lower teeth, smile, and puff out both cheeks • Assess strength of facial muscles by asking patient to close eyes tightly so they cannot be opened, and gently attempt to raise the eyelids • Observe for weakness or asymmetry

Cranial Nerve Assessment • Cranial Nerve VIII – Acoustic: Assess hearing acuity and cover one ear at a time and ask patient to repeat short test words spoken softly then louder by examiner

Cranial Nerve Assessment • Cranial Nerve IX and X – Glossopharyngeal and Vagus • Assess patient’s ability to swallow with ease; to produce saliva; and produce normal voice sounds • Instruct patient to hold breath, and assess for normal slowing of the heart rate • Testing for the gag reflex also will test the cranial nerves • Innervates abdominal viscera • Vagus is the longest cranial nerve

Cranial Nerve Assessment • Cranial Nerve XI – Spinal Accessory • Ask patient to raise and lower shoulders and to turn head • Cranial Nerve XII – Hypoglossal • Ask patient to stick out tongue and to move it in several directions

Peripheral Nervous System • Spinal Nerves – 31 pairs – Innervate muscles and organs Both sensory and motor nerves • Autonomic Nervous System – Governs internal organs • Peripheral Nervous System – Sensory Nerves • Dermatomes: areas of sensation on the skin that innervated by different spinal nerve levels • Peripheral Nervous System – Motor Nerves • Myotomes: motor nerves that innervate muscles allowing certain muscle actions

Peripheral Nervous System – Sensory Nerves • Dermatomes: areas of sensation on the skin that innervated by different spinal nerve levels – Motor Nerves • Myotomes: motor nerves that innervate muscles allowing certain muscle actions

Peripheral Nervous System • The ANS is the self governing division of the nervous system – Comprised of the Parasympathetic and Sympathetic Nervous Systems which are antagonistic to each other but balance each other out • Parasympathetic NS – Carries out normal functions • Sympathetic NS – Takes over in times of stress; works with adrenaline