Nervous System

Nervous System: Neurons Neurons are masses of nerve cells that transmit information to other nerves, tissues or cells (nerve impulses). Consists of 1. cell body- contains the nucleus and two extensions. 2. dendrites- shorter, more numerous, receive information. (carry to the cell body) 3. Axons- single, long fiber which conducts impulses away from the cell body. http://webspace.ship.edu/cgboer/theneuron.html

There are two parts to the nervous system: Central nervous system (CNS) Consists of the brain and spinal cord Peripheral Nervous System (PNS) Includes 31 pairs of spinal nerves Includes 12 pairs of cranial nerves http://www.typefreediabetes.com/Articles.asp?ID=219 http://standardnote.blogspot.com/2012/12/central-nervous-system.html

Functions of the Nervous System 1. Sensory Function- gathers information within and around the body, sends nerve impulses to the CNS. 2. Integrative function- information is interpreted, to create sensations, create thoughts, add to memory, make decisions, etc. 3. Motor Function- responds to signals (impulses). Signals go from the CNS to effectors (muscles or glands).

Brain Integration center of the body Constant input from sensory organs Constant learning Memory of response or outcome Huge collection of myelinated and unmyelinated neurons Divided into lobes: different sensory and motor functions are controlled by different lobes.

Brain Three major parts: Cerebrum: largest, sensory and motor functions, higher mental function (memory, reasoning) Cerebellum- coordinate voluntary muscles Brain stem- regulate visceral functions

Brain Sulci and gyri are along the surface Sulci are shallow grooves Gyri are ridges or bumps Fissures are deep grooves

Brain

Parietal lobe: input lobe Major sensory lobe Hard drive/memory Speech understanding-Broca’s area Recognition of people, places, items, events, etc. Memory of outcomes taste

More lobes: Occipital lobe: Temporal lobe: Cerebellum: Receives input from the eyes and sends it to the parietal lobe for interpretation Temporal lobe: receives input from the ears and sends it to the parietal lobe for interpretation memory processing –short term Cerebellum: fine motor coordination balance and posture *increases its control with practice

Brain stem 1. midbrain: 2. pons: 3. medulla oblongata: auditory and visual reflexes eye movement fluidity of movement 2. pons: integration center for cerebellum and cerebral communication respiratory center 3. medulla oblongata: involuntary muscle control autonomic reflexes respiratory/cardiovascular center vomiting, coughing, hiccupping, sneezing, swallowing

Nervous system division

Cells of the nervous System: Neurons The neuron: Large, complex cells Longevity: long life Lack centrioles- cannot perform mitosis Classified by structure and function

Parts of a neuron Cell body: contains the nucleus and all other cellular organelles along with the bulk of cytoplasm Dendrites: receptive or input regions that provide enormous surface area for receiving signals from receptor organs/glands Axon: in each neuron, there is only one! It can be very long or so short it seems nonexistent. Conduction component that generates and propagates nerve impulses away from the cell body.

More parts of a neuron…. Myelin: fatty covering that insulates the axon. Gaps between myelin are called nodes of Ranvier. 2-4 mph without myelin 250 mph with myelin Axon terminal: end of the axon where neurotransmitters are stored and released.

Functional classification of a neuron (how it reacts in the body) Sensory: receive impulses and transmit to the brain -afferent neurons Motor: receive impulses from the brain and send them to effector organs -efferent neurons Interneuron: communicate between motor and sensory along the spinal cord -association neurons

Structural Classification of a neuron Multipolar: 3 or more attachments to the cell body *** most common structure Bipolar: 2 attachments to the cell body *** rare- special senses Unipolar: 1 attachment to the cell body *** rare- PNS sensations

Cells of the nervous System: Neuroglial Cells Supportive tissue of the nervous system (more numerous than neurons) 5 types: Microglial cells Oligodendrites Astrocytes Ependymal cells Schwann cells

More neuroglia: Oligodendrocyte: in CNS Ependymal: In CNS Branching cells Wrap their branches around the neuron’s axon insulating it with myelin Ependymal: In CNS Epithelial cells Produce and form a barrier between neurons and CSF

Neuroglia Astrocyte –in CNS Microglia- in CNS Small, branching cell Most abundant neuroglia Braces neurons to capillaries- exchanges between neurons and capillaries Microglia- in CNS Thorny cells Monitors neuron health

More neuroglia: Satellite Cell: in PNS Schwann Cell: in PNS Looks like moons or satellites Job is still unknown but thought to act as astrocytes Schwann Cell: in PNS Has branching extensions like oligodendrocytes Wraps its branches around PNS neuron axons to insulate them with myelin

Nerve impulses Nerve impulse: propagation of an impulse from dendrite to axon terminal Resting membrane potential: high concentration of sodium ions outside the membrane and a high concentration of potassium inside the cell. Na/K channel vs Na/K pump: channels are open and allow ions to flow freely while pumps turn off and on to reset the membrane potential

Depolarization: neuron membrane is more permeable to sodium ions. * Na+ flows into the neuron Repolarization: neuron membrane is more permeable to potassium ions. *K+ flows out of the neuron Hyperpolarization: too much potassium leaves making the neuron too negative ~ -90mV After hyperpolarization,- sodium/potassium pumps reset the resting membrane potential.