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Chapter 10 Central & Somatic Nervous Systems Madonna High School Mr. Bob Kolanko Nervous System Central (Brain & Spinal Cord) Peripheral (Somatic & Autonomic) SNS-sensory neurons that convey information from cutaneous receptors to the CNS and motor neurons from the CNS to the skeletal muscles. Neuron Cell Body Dendrite Axon Myelinated (white matter) Lipid and protein covering, speeds up impulse & aids in regeneration (only in the PNS) Unmyelinated (gray matter) Spinal Cord Protection- well protected Vertebral column, rounded bone Meninges Cerebrospinal fluid Vertebral ligaments Meninges- connective tissue Dura mater: outermost layer Tough, dense irregular CT Runs from L2 to and around the brain. Arachnoid: middle layer Spider-like arrangement of collagen & elastic fibers Pia mater: innermost layer Transparent Collagen & elastic fibers Numerous blood vessels Meninges Epidural Space- Between dura mater vertebral canal Inject anesthetic- epidural block Fat and connective tissue Subdural space- between dura mater and arachnoid. Subarachnoid space- between arachnoid and pia mater. Where cerebrospinal fluid circulates 16 to 18 inches long Begins at the brain stem (medulla oblongata) Cauda equina- “horse hairs” lower portion of the SC. Two cords Cervical Enlargement- supplies nerves to the upper limbs Lumbar Enlargement- supplies nerves to the lower limbs Spinal Segments 31 segments with a pair of spinal nerves each 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal Spilt into two halves Separated by two fissures Anterior median fissure- deeper of the two Posterior median fissure Forms “H” shape, gray matter surrounded by white matter. Horns Central canal White Matter Aligned into 4 columns Anterior Posterior Lateral (2) Sensory Tracts- ascending Motor Tracts- decending Gray Matter: Receives and integrates incoming and outgoing impulses. White Matter: Conducts impulses up and down the spinal cord. Pathways Direct pathways: convey nerve impulses that cause precise voluntary movement of the skeletal muscles. Lateral corticospinal Anterior corticospinal Corticobulbar Pathways Indirect pathways: Convey impulses that program automatic movements, help coordinate body movements with visual stimuli, maintain skeletal muscle tone and posture. Spinal Nerves Posterior (dorsal) root- sensory nerve fibers Conducts impulses from the periphery to the SC. Dorsal root ganglion- swelling which contain the cell bodies of the sensory neurons from the periphery. Anterior (ventral) root- motor nerve axons Conducts impulses from the SC to the periphery. The cell bodies are located in the grey matter. Reflex Center: the spinal cord serves as an integrating center for spinal reflexes. Reflexes- fast, predictable, automatic responses to changes. Reflex Arc: Receptor- dendrite, receives stimuli and produces the impulse. Sensory neuron- conducts impulses from receptors to integrating center. Integrating center- association neurons. Motor neuron- conducts impulses from IC to effector. Effector- muscle the responds to motor nerve impulse Reflexes Somatic reflexes: reflexes that result in the contraction of skeletal muscles. Patellar reflex- knee jerk Helps us stand erect despite gravity. Withdrawal reflex- immediate withdrawal from a painful stimulus. Autonomic reflexes: reflexes that regulate smooth and cardiac muscles as well as many glands. Spinal Nerves 31 Pairs C1 – C8 T1 – T12 L1 – L5 S1 – S5 Co1 Leave through the intervertebral foramina between the vertebrae. Spinal Nerves Two attachment points to the SC. Posterior root Anterior root The two roots come together to form a “mixed” spinal nerve. Bundles of fibers wrapped in CT and blood vessels. Spinal Nerves After the spinal nerves leave the intervertebral foramen, they divide into branches, “Rami” Dorsal ramus- deep muscles and skin of the back Ventral ramus- superficial back muscles, structures of the limbs and the lateral & ventral trunk. Spinal Nerves Plexuses- ventral rami form a network of adjacent nerves. Cervical plexus- skin and muscles of the head, neck, shoulders… Brachial plexus- supply upper limbs Lumbar plexus- abdominal wall, genetals, lower limbs Sacral plexus- buttocks and lower limbs Sciatic nerve Intercostal Nerves T2 – T11 Do not form a plexus Go directly to the structures that they supply Muscles between the ribs Abdominal muscles Skin of the chest and back The Brain One of the largest organs in the body. 100,000,000,000 neurons Weighs 3 lbs. The Brain Four principal parts Brain stem Medulla oblongata Pons Brain stem Diencephalon Thalamus hypothalamus The Brain Four principal parts Cerebrum Two sides Cerebellum “Cauliflower” The Brain Cranial meninges- extension of the spinal meninges Dura mater Arachnoid Pia mater The Brain Cerebrospinal Fluid (CSF) Circulate through the subarachnoid space. 80 to 150 ml Flows through the ventricles of the brain Ventricles Cavities within the brain connected together. Lateral ventricles (2) Third ventricle Fourth ventricle The Brain Cerebrospinal Fluid (CSF) Purpose Shock absorber The brain floats within the fluid Delivers nutrients and removes waste and toxic substances. The Brain Cerebrospinal Fluid (CSF) Fluid is constantly being created and absorbed. Produced in the ventricles Absorbed in the superior sagittal sinus by the arachnoid villi. If an obstruction occurs and you have a build up of CSF one develops “hydrocephalus”. The Brain Blood supply The brain requires 20% of the body’s oxygen. Most metabolic organ of the body, oxygen use increases with mental activity. Cerebral arterial circle “Circle of Willis” Special circulatory route at the base of the brain. The Brain Blood supply If oxygen is deprived for 4 or more minutes, permanent injury can occur. Lysosomes will break open and release enzymes that destroy the brain cells. The brain cannot store carbohydrates. If blood has low glucose levels, mental confusion, dizziness, convulsions and loss of consciousness. The Brain Brain Stem: Medulla- continuation of the spinal cord, inferior part of the brain stem. Contain sensory and motor tracts, white matter. Pyramids- large motor and sensory tracts Fibers cross from the right to left sides and visa versa. Decussation of pyramids… why the right half of your brain controls the left side of your body. Cardiovascular center- regulates the rate and force of the heartbeat. The Brain Brain Stem: Medulla Regulates basic breathing Coordinates Swallowing Vomiting Coughing Sneezing Hiccups The Brain Brain Stem: Pons- “bridge” Above the medulla and in front of the cerebellum. Connects the parts of the brain with each other. Midbrain- Cerebral peduncles- Motor tracts connecting the cerebral cortex to the pons. Sensory tracts between SC and the thalamus. The Brain Diencephalon Thalamus Above the midbrain Mainly gray matter Relay station for sensory impulses from other parts of the CNS to the cerebral cortex. The Brain Diencephalon Hypothalamus Below the thalamus Controls and integrates the autonomic nervous system. Controls the release of hormones Controls normal body temperature Feelings of rage, aggression, pain and pleasure Regulates food and liquid intake Maintains consciousness and sleep paterns. The Brain Diencephalon Reticular Activating System (RAS), Consciousness and Sleep. Regulate 24 hour sleep cycle. Arousal of the RAS awake sleep The Brain Cerebrum- the bulk of the brain. Surface is a thin layer of gray matter “cerebral cortex” Below that is the cerebral white matter. Gray matter grows faster than white matter during embryonic development rolls and folds. The Brain Cerebrum Fold are called “gyri” Deep grooves are “fissures” Longitudinal fissure- separates into two halves. Connected by the corpus callosum Larger in females…greater emotion. Shallow grooves are “sulci” The Brain The hemispheres The two halves or hemispheres may look almost identical but one is usually slightly more developed. The dominant side is where written and spoken language is organized. In almost all of us, the left hemisphere is dominant for this job, even if you are right-handed. Because of the “cross-over” design of the nervous system, the right side of your brain controls the left side of your body, and vice versa. The Brain The hemispheres Right hemisphere The right side of the brain controls artistic functions such as music, awareness of art and insight. It also controls the ability to understand spatial relations, recognize faces and focus your attention on something. People with a stroke on the right side may have trouble with these functions. Left hemisphere The left side of the brain is responsible for scientific function, such as the ability to work with numbers (mathematical skills) and reasoning. It also is largely responsible for the ability to understand spoken language and the written word. The Brain The lobes Frontal Lobe responsible for movement (motor functions). Occipital lobe: Responsible for vision. The Brain The lobes Parietal lobe: Behind the frontal lobe lies the parietal lobe. It is concerned mainly with sensory activities, such as receiving and interpreting information from all parts of the body. Temporal lobe: Controls hearing and memory and is also involved with auditory perception. Memories are stored in the inner part of the temporal lobe. The Brain EEG Electroencephalogram Records the electronic brain waves. Diagnosis of epilepsy, tumors, blood clots… Criteria for brain death. The Brain Cerebellum nd 2 largest portion of the brain. Behind the medulla and below the occipital lobe. Two cerebellar hemispheres Surface Cerebellar cortex Grey matter Below the surface is white matter Below the white matter is more grey matter Cerebellar nucli The Brain Cerebellum Compares the intended movement of the motor areas of the cerebrum with what actually happened. Constantly is receiving stimuli from muscles, tendons, and joints. Smooths and coordinates complex sequences of skeletal muscle contractions. Regulates posture and balance. Damage to cerebellum Staggering or abnormal walking movement Severe dizziness. The Brain Neurotransmitters 60 substances know to be neurotransmitters Released by the synaptic vesicles Established lines of communication between nerve cells. CNS depends on proper levels to regulate activity. The Brain Neurotransmitters Acetylcholine Cerebral cortex, skeletal neuromuscular junction and ANS. Excitatory Dopamine Brain Excitatory, involved in emotional response and subconscious movements of the skeletal muscles. The Brain Neurotransmitters Norepinephine Released at neuromuscular and neuroglandular junctions Found in the CNS Related to arousal, dreaming and regulation of mood. Serotonin CNS Inhibitory Induces sleep, sensory perception, temp. regulation and control of mood. The Brain Neurotransmitters GABA Brain Inhibitory Target of antianxiety drugs Substance P Sensory nerves and CNS Stimulates perception of pain The Brain Neurotransmitters Enkephalins CNS Inhibits pain impulses by supressing substance P. Endorphines Pituitary gland and brain Inhibits pain by inhibiting substance P. Memory and learning, Sexual activity, control body temp.
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