Intro to nervous system Flashcards
What are the functions of the nervous system?
Sensory input, integration, motor output
Sensory input
monitoring stimuli occuring inside and outside the body
Integration
Processing of sensory input and formulation of motor commands
Motor output
Response to stimuli by activating effector organs
What does the nervous system consist of?
Central nervous system (brain and spinal cord) and peripheral nervous system ( all nervous tissue outside the CNS)
Reflex
Predictive rapid response to a stimulus
- Receptor detects stimulus
- afferent/sensory neuron relays info to the CNS *control/integration center (region of the CNS that processes sensory info and sends motor commands)
- Efferent/motor neuron carries motor commands away from CNS to the effector
- effector (muscle or gland that responds to motor commands by producing the response)
Afferent/ sensory division of PNS
Carry info from receptors to the CNS
Somatic afferent fibers
Carry impulses from skin, skeletal muscles and joints
Visceral afferent fibers
Carry impulses from organs within ventral body cavities
Special sensory afferent fibers
Carry impulses from nose, eye, tongue, and ear
Efferent/motor division of PNS
Motor neurons carry commands away from CNS to effectors
Somatic efferent fibers
control voluntary skeletal muscle contraction
Autonomic efferent fibers
Control involuntary cardiac muscle, smooth muscle and glands
Sympathetic division
travels through thoracic and lumbar spinal nerves and produces the fight or flight responses to mobilize energy reserves and prepare for activity to deal with stress
Parasympathetic division
Travels through cranial nerves and sacral spinal nerve and produces the rest and digest maintenance responses to store and conserve energy
Structure of a typical neuron
- Soma-cell body, contains nucleus and organelles
- Dendrites-branching extensions that contain receptors to detect neurotransmitters from other neurons
- Axon hillock- where cell body tapers into the axon, site where the action potential originates
- Axon-single long process, transmits action potential away from soma
- Axolemma-Plasma membrane of an axon
- Myelin sheath-Insulation formed by glial cells wrapping around the axon, nodes of ranvier-gaps in myelin sheath, internodes-segements of myelin
- Axon terminals-enlarged distal ends of an axon that contain secretory vesicles filled with neurotransmitters (synaptic vesicles)
Interneurons (association neurons)
create neural circuits enabling communication between sensory or motor neurons and the CNS, only found in CNS
Multipolar neuron
multiple processes branching off the cell body, numerous dendrites and one axon
Pseudounipolar neuron
appear to have one extension off the cell body. This extension branches forming a long axon with dendrites on one end and axon terminals on the opposite end *most sensory neurons of the PNS
Bipolar neuron
Two extensions from cell body, one dendrite and one axon *Found in special sense organs
Neuroglia (glia)
cells that surround and support neurons
Astrocyte (CNS)
Star shaped, processes cling to neurons and capillaries
- Provide structural support-anchor neurons to surrounding tissues and capillaries
- Maintain blood brain barrier-feet wrap around capillaries and controls uptake of selected materials from the blood
- Adjusts interstitial environment-recaptures released neurotransmitters and leaked ions
- Guides neuron development-directs growth of neurons and synapse formation
Oligodendrocyte (CNS)
Wrap cytoplasmic processes around the axons of neurons
*Forms a white fatty insulation material called a myelin sheath
Microglial cells (CNS)
Oval cells with long thorny processes
*Remove cellular debris and pathogens
Ependymal cells (CNS)
Ciliated cells, line chambers filled with CSF
- Monitor and maintain the composition of CSF
- Assist in circulation of CSF
Schwann cells (PNS)
Surrounds and protects axons in PNS
- Forms myelin sheath around some axons of PNS
- Neurilemma-outer layer that contains schwann cell cytoplasm
Satellite cells (PNS)
Surround cell bodies of neurons
*Isolates cell body and regulates exchange of nutrients and waste
Membrane potential
Separation of charge across the plasma membrane measured in volts
Resting membrane potential
Membrane potential at rest when the cell is not receiving information in the form of a graded potential of sending out information as an action potential. Resting potential is typically around -70mV *Chemical gradients-higher Na+ outside cell, higher k+ inside cell
Depolarization
The membrane potential becomes less negative
*When neurons are stimulated Na+ channels open and Na+ rushes into the cell
Graded potential
A localized change in membrane potential that is short lived and dissipates as it travels
- Can be stimulated by neurotransmitters binding to ligand gated channels, mechanical stress, or temperature change
- If the stimulus is excitatory it will cause depolarization of the membrane
Action potential
Electrical impulse producing a brief reversal of the membrane potential that travels down the entire length of the axon from the axon hillock to the axon terminals
Rising (depolarization) phase of the action potential
Na+ rushes in through voltage gated Na+ channels
Threshold potential
V-gated Na+ channels open at membrane potential of -55mV
Falling (Repolarization) phase of action potential
K+ rushes out through voltage gated K+ channels
Synapse
Junction between two neurons or a neuron and muscles, glands, or cells
Structure of a synapse
- Presynaptic neuron-transmits impulse towards synapse, axon terminals of the presynaptic neuron release neurotransmitters
- Synaptic cleft-fluid filled space where neurotransmitters are released
- Postsynaptic cell (Neuron, muscle, gland, etc)-receives information from the presynaptic neurons
