NERVOUS SYSTEM FUNCTION

NEURON FUNCTION Transmit messages from one cell to the next Dendrites carry impulse to the cell body Axons carry impulse away from cell body Neurilemma (myelin sheath) Covering that speeds up nerve impulse along axon Fatty substance that protects axon called myelin and white matter

Neuron function continued Synapse Space between neurons Neurotransmitter Chemicals that carry an impulse across the synapse Nerve impulse A stimulus creates an impulse. The impulse travels into the neuron on the dendrite(s) and out on the axon. At the end of the axon, a neurotransmitter is released that carries the impulse across the synapse, to the next dendrite.

NERVOUS TISSUE Sensory neurons (afferent) Motor neurons (efferent) Carry impulses from skin and sense organs to spinal cord and brain Motor neurons (efferent) Carry messages from brain and spinal cord to muscles and glands Associative neurons (interneurons) Carry impulses from sensory neurons to motor neurons

brain Part of the Central Nervous System (CNS) Brain tissue will die in 4-8 mins without oxygen Meninges Dura mater – outer brain covering; lines the inside of the skull tough, dense fibrous connective tissue Arachnoid – middle layer Resembles a fine cobweb with fluid filled spaces Pia mater – covers the brain itself Consists of blood vessels held together by fine areolar connective tissue Subdural space – between arachnoid and dura mater Subarachnoid space – between arachnoid and pia mater, filled with cerebrospinal fluid, acts as liquid shock absorber and source of nutrients for brain.

brain continued Ventricles – 4 cavities Cerebral ventricles 2 largest located in cerebral hemisphere: right and left lateral ventricles Third ventricle is behind and below the lateral ventricles Fourth ventricle is below the third, in front of the cerebellum and behind the pons and medulla oblongata 1st two and 3rd connected via the interventricular foramen 3rd and 4th connected via cerebral aqueduct

Ventricles continued Cerebrospinal fluid fills ventricles and acts as shock absorber Blood-brain barrier – prevents substances (like drugs) from penetrating brain tissue, but also makes infections like meningitis difficult to cure Choroid plexus – blood vessels that help make cerebrospinal fluid Part of the pia mater In contact with the cells lining the ventricles Have selective permeability

Cerebrospinal fluid (CSF) Forms inside the ventricles from the choroid plexus Formed by filtration Transports nutrients to and removes metabolic waste products from the brain cells Flows from 2 lateral ventricles to 3rd ventricle to 4th and finally to spinal cord and subarachnoid spaces Eventually it returns to the bloodstream via the venous structures in the brain called arachnoid villi

Cns – brain - cerebrum Responsible for conscious thought, judgment, memory, reasoning, and will power Largest part of the brain Occupies the whole upper part of the skull Weighs about 2 lbs. Cerebral cortex: gray matter covering the upper and lower surfaces Divided into 2 hemispheres by a deep groove – longitudinal fissure Covered with furrows and ridges Deep are fissures Shallow are sulci

diencephalon Thalamus Hypothalamus Found in cerebral hemispheres Relay station for incoming or outgoing nerve impulses Receives nerve impulses from sense organs and brain Damage may result in increased sensitivity to pain or total loss in consciousness Hypothalamus Lies below the thalamus Considered the “brain” of the brain Stimulates pituitary to release hormone

HYPOTHATLAMUS VITAL FUNCTIONS ARE: ANS control Cardiovascular control Temperature control Appetite control Water balance Manufacture of oxytocin GI control Emotional state Sleep control Mind-over body experiences

Brain continued Cerebellum (controls ALL functions w/skeletal muscles) Maintenance of balance Maintenance of muscle tone Control of muscle movements BRAIN STEM (made up of 3 parts): Pons Controls respiration Midbrain Vision and hearing Medulla oblongata Controls heart rate and blood pressure

Cns (which is what?) SPINAL CORD Surrounded by cerebrospinal fluid Conducts nerve impulses to and from brain Acts as reflex center

PERIPHERAL NERVOUS SYSTEM Cranial nerves How many pairs? Spinal nerves REMEMBER ANY OF THIS???

TO REFRESH YOUR MEMORY: Cranial nerves 12 pairs beginning in the brain Mainly deal with functions of the head and neck Except vagus nerve (X) – responsible for ___ (pg. 175) Designated by name and number Name can give a clue to function Spinal nerves 31 pairs originating at the spinal cord Exit through openings in the vertebrae Named according to region and level they exit Largest is the sciatic nerve

AUTONOMIC NERVOUS SYSTEM Regulates visceral organs, no subject to conscious control Sympathetic system Fight or flight – when the body perceives danger, SNS sends message to adrenal medulla to secrete adrenaline and heartbeat increases Parasympathetic system Counters SNS, decreases heart rate Reflex – unconscious and voluntary Stimulus Example: tapping the patellar tendon What are some other examples?