Nervous

Function command unit provides senses sends signal between body and brain Responds to internal and external stimuli

Neuron Dendrite- impulse passes here 1 st Cell Body Axon- covered in myelin- acts as insulator, “white matter”-end at axon terminal

3 types of neurons Sensory- carries impulse from body to brain or spinal cord Motor- carries impulse from brain to muscle or gland cell(target cell) Interneuron- connects brain to spinal cord

Impulse moves dendrite  cell body  axon  target cell How does impulse move along axon? Neurons have a charge(-70 mv) on the cell membrane.This is due to more + ions on the outside of the cell than on the inside. Neurons are excitable- charge can change This is called action potential- ability of membrane to  or  charge.

Normal conditions of cell More K + inside More Na+ outside This is the resting potential of a cell The cell is Polarized because of the charge difference.

Impulse cause Na+ to rush into cell (DEPOLARIZATION) through ion gates K+ pushed out of cell Cell tries to bring back to normal Push Na+ out Push K+ back in(Reploarized) Causes impulse to move down membrane to next ion gate

How does impulse travel so quickly? Axon covered with an insulator –MYELIN- “White matter” Impulse jumps from node to node

ALL OR NONE THEORY An impulse has only 1 strength It must be strong enough to start an impulse in a sensory organ or reach the threshold level. If it reaches the TL then the impulse is transmitted, if not- no transmission

How does impulse jump from axon to next nerve or cell? Need to make connection between neuron and empty space. 1. Vesicles filled with neurotransmitter 2. Vesicles fuse with membrane 3. Neurotransmitters released into synapse 4. Neurotransmitter binds to receptor site on next neuron or target cell 5. Depolarization occurs in cell #2 6. Ion gates (K+ and Na+) open up 7. Impulse transmitted

Synapse

There are 2 parts to your nervous system Central Nervous system- Spinal cord + brain Peripheral Nervous System- All nerves coming from cord

Brain Protected in 3 ways: 1. Skull 2. Wrapped in connective tissue: Meninges 3 layers- inner-pia matter middle- arachnoid outer-dura matter 3. Cerebrospinal fluid- found between pia matter and arachnoid layers and serves as a shock absorber Brain must have constant supply of oxygen!!!

BRAIN Cerebrum Brain Stem Cerebellum

Cerebrum: Site of Intelligence,Memory,Language Movement of skeletal muscle(voluntary) 2 halves- left brain/right brain Connected by CORPUS COLLOSUM- thick band of connective tissue(So both sides can talk to each other) Each hemisphere is divided into 4 lobes: frontal, parietal, occipital, and temporal. Has folds or convolutions to add surface area. 2 surfaces: Cerebral cortex or grey matter is the outer surface Cerebral medulla- white matter is the inner surface that contains myelinated axons.

Brain Stem : 3 parts- connects brain to cord Medulla Oblongata- breathing/ heart rate/swallowing Pons -above medulla, links cerebral cortex and cerebellum Midbrain -involved in hearing and vision

Cerebellum: Balance Posture Coordination

Two other parts of the brain are found between brainstem and cerebrum Hypothalmus-control center for hunger, thirst, fatigue, anger, and temperature Thalmus- switching station for sensory input, passes info to cerebrum

Brain is a source of weak electrical activity that can be detected by an EEG(electroencephalogram) Sleep is when the cerebral cortex falls to its lowest possible level Memory is thought to be short and long term

THE SPINAL CORD Emerges from the base of the skull Protected by bone, the vertebral column or backbone; also the meninges and cerebrospinal fluid. Links the brain with the peripheral nervous system. Carries impulses to and from the brain and regulates reflexes. A reflex is a response to a stimulus. 31 pairs of spinal nerves branch out to the body from the spinal cord.

The spinal cord consists of 2 kinds of nerve tissue: 1.Central part is H shaped and consists of gray matter 2.Outer part is the white matter and consists of myelinated axons. Sensory neurons carry impulses from receptors to the spinal cord. Motor neurons carry impulses from the spinal cord to the effectors (glands/muscles). Interneurons connect the sensory and motor neurons.

2 parts Sensory division- transmits impulses from sense organs to CNS Motor Division- transmits impulses from CNS to the effector(muscle, glands) This has 2 subdivisions: Peripheral Nervous System

Somatic 12 pairs of cranial nerves voluntary 31 pairs of spinal nerves Also controls reflexes- bypasses brain- signal goes directly to spinal column sensory nerve  spinal column  motor nerve  target cell

Autonomic - automatic carries impulse from CNS to internal organs Involuntary Sympathetic- controls during time of stress “Fight or Flight”-increase heart rate, breathing, temp,blood pressure Parasympathetic- bring back to normal Control during rest

Sensing Chemicals Chemoreceptors in mouth and nose Nose receptors- sense chemicals –impulse carried on Olfactory Nerve- sent to brain Mouth receptors- taste buds on tongue (10,000) Sweet, sour, salty, bitter

Eye consists of 3 layers: 1. outer layer contains the sclera or white of the eye which consists of tough connective tissue and the cornea which is the transparent covering of the eye. Between the cornea and the sclera is the aqueous humor, a clear fluid. 2. middle layer is the choroid that contains the iris (colored part of the eye) which has an opening called the pupil. Just behind the pupil is the lens, that refracts incoming light. The eyeball itself consists of a large chamber filled with jellylike fluid, the vitreous humor. 3. inner layer is the retina located at the very back of the eye and contains light sensitive cells called photoreceptor cells. This is the place where light energy is converted into electrical impulses.

Sensing light- These cells contain the pigment rhodopsin which is sensitive to different wavelengths of light. These cells fall into 2 groups; Rods sense light and dark and the Cones sense color. It is in these cells where light is converted into impulses that then travel to the brain via the optic nerve.

Mechanical Stimulation Hearing- detect vibrations, sound waves Outer ear consist of auditory canal-collects vibrations Sound waves hit tympanic membrane (eardrum) Ear drum vibrates Vibration passed to 3 bones- malleus, incus, stapes Vibration passed to oval window- causes fluid in cochlea to vibrate This causes little hairs in cochlea to bend Sends impulse to brain via auditory nerve Brain interprets

Balance- center located in inner ear Sends info to brain Semicircular canal filled with fluid and hairs and ear stones(otoliths-CaCO2) Stones lay on hairs Hair bends- stimulates nerve Sends impulse to brain

Touch- receptors in dermis Feel temperature, pressure, pain Receptors located in specific areas Light touch- tips of fingers, eyelids, mouth Heavy touch- joints, muscles, palms Free nerve endings- itch, tickle, hot, cold, pain Pain- all over body, except brain Heat- deep in dermis Cold- near surface