CENTRAL NERVOUS SYSTEM. Sensory Pathway (PNS) OVERVIEW OF SPINAL CORD ANATOMY OF THE SPINAL CORD FUNCTIONS OF THE SPINAL CORD

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1 CENTRAL NERVOUS SYSTEM Central nervous system (CNS) brain and spinal cord enclosed in bony coverings Functions of the spinal cord spinal cord reflexes integration ti (summation of inhibitory and excitatory) t nerve impulses highway for upward and downward travel of sensory and motor information Brain functions sensations, memory, emotions, decision making, behavior INCOMING INFORMATION-RECEPTORS Respond to stimuli: nerve endings (dendrites of neurons) sense organs (taste) Sensory Pathway (PNS) Afferent neurons somatic and visceral sensory neurons MOTOR PATHWAY (PNS) Efferent neurons Stimulate and control effectors somatic motor neurons visceral motor neurons Autonomic Nervous System (ANS) Sympathetic Parasympathetic They both control the same effectors (with few exceptions) but have opposite responses in the effectors OVERVIEW OF SPINAL CORD Information highway between brain and body Each pair of spinal nerves receives sensory information and issues motor signals to muscles and glands Spinal cord is a component of the CNS while the spinal nerves are part of the PNS FUNCTIONS OF THE SPINAL CORD Conduction bundles of fibers passing information up and down spinal cord Locomotion repetitive, coordinated actions of several muscle groups central pattern generators are pools of neurons providing control of flexors and extensors (walking) Reflexes involuntary, stereotyped responses to stimuli (remove hand from hot stove) involves brain, spinal cord and peripheral nerves ANATOMY OF THE SPINAL CORD Cylinder of nerve tissue within the vertebral canal (thick as a finger) vertebral column grows faster so in an adult the spinal cord only extends to L1 31 pairs of spinal nerves arise from cervical, thoracic, lumbar and sacral regions of the cord each cord segment gives rise to a pair of spinal nerves

2 MENINGES OF THE SPINAL CORD MENINGES OF VERTEBRA AND SPINAL CORD 3 Fibrous layers enclosing spinal cord Dura mater tough collagenous membrane surrounded by epidural space filled with fat and blood vessels epidural anesthesia utilized during childbirth Arachnoid mater layer of simple squamous epithelium lining dura mater and loose mesh of fibers filled with CSF (creates subarachnoid space) Pia mater delicate membrane adherent to spinal cord CROSS-SECTIONAL ANATOMY OF THE SPINAL CORD AREAS IN THE SPINAL CORD Pair of dorsal or posterior horns dorsal root of spinal nerve is totally sensory fibers Pair of ventral or anterior horns ventral root of spinal nerve is totally motor fibers Connected by gray commissure punctured by a central canal continuous above with 4th ventricle Central area of gray matter shaped like a butterfly and surrounded by white matter in 3 columns Gray matter = neuron cell bodies with little myelin White matter = myelinated axons WHITE MATTER IN THE SPINAL CORD White column = bundles of myelinated axons that carry signals up and down to and from brainstem 3 pairs of columns or funiculi dorsal, lateral, and anterior columns Each column is filled with named tracts (fibers with a similar origin, destination and function) Ascending and descending tract head up or down Contralateral means origin and destination are on opposite sides while ipsilateral means on same side REFLEXES Automatic response to change in environment Integration center for spinal reflexes is gray matter of spinal cord Examples somatic reflexes result in skeletal muscle contraction autonomic (visceral) reflexes involve smooth & cardiac muscle and glands. heart rate, respiration, digestion, urination, etc Reflexes can be: simple involve peripheral nerves and the spinal cord spinal reflexes learned (acquired) involve peripheral nerves and the brain

3 REFLEX ARC Specific nerve impulse pathway 5 components of reflex arc Receptor Registers stimuli Sensory neuron Transmits stimuli to the CNS Integrating center Part of the CNS that processes the information and generates response Motor neuron Transmits the response to the effector Effector Muscle or gland 4 important somatic spinal reflexes stretch, tendon, flexor(withdrawal) & crossed extensor reflexes THE PATELLAR TENDON REFLEX ARC CENTRAL NERVOUS SYSTEM-THE BRAIN THE BRAIN Longitudinal fissure - cerebral hemispheres. gyri = folds; sulci = grooves cortex = surface layer of gray matter nuclei = deeper masses of gray matter tracts = bundles of axons (white matter) MEDIAN SECTION OF THE BRAIN GRAY AND WHITE MATTER Gray matter = neuron cell bodies, dendrites, and synapses forms cortex over cerebrum and cerebellum forms nuclei deep within brain White matter = bundles of axons forms tracts that connect parts of brain

4 MENINGES OF THE BRAIN VENTRICLES AND CEREBROSPINAL FLUID Internal chambers within the CNS lateral ventricles in cerebral hemispheres third ventricle = single vertical space under corpus callosum cerebral aqueduct runs through midbrain fourth ventricle = chamber between pons and cerebellum central canal runs down through spinal cord Lined with ependymal cells Choroid plexus produce CSF BRAIN VENTRICLES CEREBROSPINAL FLUID Fills ventricles and subarachnoid space Brain produces and absorbs 500 ml/day choroid plexus creates by filtration of blood Functions floats brain so it is neutrally buoyant cushions from hitting inside of skull chemical stability -- rinses away wastes Escapes (4th ventricle) to surround brain Absorbed into venous sinus by arachnoid villi HINDBRAIN - MEDULLA OBLONGATA Cardiac center adjusts rate and force of heart Vasomotor center adjusts blood vessel diameter Respiratory centers control rate and depth of breathing Reflex centers for coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head Most of the fibers are crossing over Left cortex controls right side of body PONS Bulge in brainstem, superior to medulla Ascending sensory tracts Descending motor tracts Pathways in and out of cerebellum Nuclei concerned with posture, sleep, hearing, balance, taste, eye movements, facial expression, facial sensation, respiration, swallowing, and bladder control

5 CEREBELLUM Two hemispheres connected by vermis Cortex = surface folds called folia Output comes from deep gray nuclei granule and purkinje cells CEREBELLUM White matter (arbor vitae) visible in sagittal section Evaluation of sensory input coordination and locomotor ability spatial perception Timekeeping center predicting movement of objects MIDBRAIN - CROSS SECTION Tegmentum connects to cerebellum and helps control fine movements through red nucleus Substantia nigra sends inhibitory signals to basal ganglia and thalamus (degeneration leads to tremors and Parkinson disease) Central gray matter = pain awareness RETICULAR ACTIVATING SYSTEM Scattered nuclei in medulla, pons & midbrain Reticular activating system alerts cerebral cortex to sensory signals (sound of alarm, flash light, smoke or intruder) to awaken from sleep maintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and muscles Motor function is involvement with maintaining muscle tone DIENCEPHALON: THALAMUS AND HYPOTHALAMUS Thalamus Functions Relays signals from cerebellum to motor cortex Emotional and memory functions Hypothalamus Functions hormone secretion autonomic NS control thermoregulation food and water intake (hunger and satiety) sleep and circadian rhythms memory (mammillary bodies) emotional behavior CEREBRUM -- GROSS ANATOMY Cerebral cortex - 3mm layer of gray matter extensive folds increase surface area - divided into lobes

6 FUNCTIONS OF CEREBRUM - LOBES Frontal voluntary motor functions planning, mood, smell and social judgement Parietal receives and integrates sensory information Occipital visual center of brain Temporal areas for hearing, smell, learning, memory, emotional behavior TRACTS OF CEREBRAL WHITE MATTER Most of cerebrum is white matter Types of tracts projection tracts from brain to spinal cord, forms internal capsule commissural tracts cross to opposite hemisphere corpus callosum anterior and posterior commissures association tracts connect lobes and gyri within a hemisphere LIMBIC SYSTEM Loop of cortical structures amygdala, hippocampus and cingulate gyrus Role in emotion and memory pleasure and aversion centers MEMORY Information management requires learning, memory and forgetting Amnesia anterograde amnesia - no new memories retrograde amnesia can t remember old ones Hippocampus organizes sensory and cognitive information into a new memory Cerebellum helps learn motor skills Amygdala - emotional memory AUTONOMIC NERVOUS SYSTEM Visceral motor neurons control heart rate breathing rate digestion blood pressure salivation Nerve impulses of these motor neurons start in the CNS (medulla oblongata and pons) Pathway through: Spinal cord Cranial nerves SYMPATHETIC DIVISION The sympathetic division is called the fight or flight system when the body needs to generate energy exercise, excitement, emergency, and embarrassment Fight or flight response increases heart rate, blood pressure, respiration rate, blood flow to skeletal muscles, glucose metabolism decreases the activities that are not essential at the moment (digestive system organs are subdued- decreased blood flow to that system

7 PARASYMPATHETIC DIVISION The parasympathetic division is called the rest and digest activated when the body needs to conserve energy digestion, defecation, and diuresis (urination) Promotes necessary changes during these activities decreases heart rate, blood pressure, respiration rate, blood flow to skeletal muscles, glucose metabolism increases the activity of and blood flow to the digestive system organs ORGANIZATION OF THE SYMPATHETIC DIVISION EFFERENT SYMPATHETIC VS. PARASYMPATHETIC EFFECTS OF NEUROTRANSMITTERS OF THE AUTONOMIC NERVOUS SYSTEM The cells of each organ controlled by the ANS have both ACh and NE receptors organs are dually controlled The response of the organ is determined by the identity of the neurotransmitter released the binding of ACh to its receptor will cause the effector to respond in one way the binding of NE to its receptor will cause the effector to respond in the opposite way The effect of ACh and NE is effector specific NE increases heart rate, ACh decreases heart rate NE decreases the secretion of saliva, ACh increases the secretion of saliva