Friday - 3/11/16 Question of the Day Agenda In a neuron, what are the functions of dendrites and the myelin sheath? Microglial cells dispose of debris by using the process of _____. Review Nerve impulse notes Nerve impulse activity
Basic functions of the nervous system Sensory – gathers info Integrative – information is brought together Motor – responds to signals, restores homeostasis
Organization of the nervous system
Organization of the nervous system Subdivision composed of the brain and spinal cord? Subdivision of the PNS that controls voluntary activities? Nervous system subdivision composed of cranial and spinal nerves? Subdivision of PNS that regulates the activity of the heart and smooth muscle? Subdivision that interprets incoming information? Subdivision that carries impulses from the CNS to organs, glands and muscles?
Nervous tissue: structure and function Supporting Cells (Neuroglia) Astrocytes (anchor to nutrient supply lines, forms blood-brain barrier) Microglia (dispose of debris) Ependymal cells (protective cushion (CSF) around CNS – line cavities of brain and spinal cord) Oligodendrocytes (produces myelin sheath) Neurons Nerve cell Transmits messages (nerve impulses)
Structure of a neuron
Structure of a neuron Cell body: contains the nucleus Dendrites: Receive incoming messages (toward cell body) – may have hundreds Axon: Conducts impulses away from the cell body – 1 per neuron
Structure of a neuron Myelin sheath: wraps the axon to insulate and speed up the rate of nerve impulse transmission Schwann cells: produce myelin (in the PNS (motor neurons) Node of Ranvier: gap in insulation, speeds up action potential
Structure of a Neuron Axon terminal: end of axon – has vesicles that holds neurotransmitters Synapse: junction separating the axon terminal – where NT’s are released into
Multiple sclerosis Multiple Sclerosis
Nerve impulse conduction Na - In (15) Out (150) K - In (140) Out (5) Nerve impulse conduction An inactive neuron is at its resting membrane potential The inside of the cell is more negatively charged than the outside of the cell (channels are closed) Na ions outside/ K ions inside Plasma membrane is relatively impermeable to both Na and K
Nerve impulse conduction When a neuron is stimulated by an action potential (nerve impulse) the permeability of the plasma membrane changes for a short period of time. Sodium channels open and sodium ions diffuse into the cell = DEPOLARIZATION Action potential travels length of axon (all or nothing) when threshold is reached
Nerve impulse conduction After sodium ions enter the cell, the permeability changes again and becomes impermeable to sodium, but permeable to potassium K ions diffuse out of the neuron which restores the electrical conditions at resting membrane potential = REPOLARIZATION Another action potential cannot be conducted without repolarization
Nerve impulse conduction After repolarization, the sodium potassium pump restores the concentration of Na and K inside and outside of the neuron Requires ATP
Nerve impulse conduction animation Why does my foot fall asleep?
impulse transmission at synapse Action potential reaches the axon terminal where vesicles release neurotransmitters
Impulse transmission at synapse NT’s diffuse across the synapse and bind to receptors on the membrane of the next neuron If enough NT is released, the whole series (depolarization…) will occur leading to the nerve impulse traveling down the neuron
Neurotransmitters released Acetylcholine Epinephrine/Norepinephrine Dopamine Serotonin
Reflexes
Reflexes Rapid and involuntary responses to stimuli Occur in pathway called reflex arc 2 types Somatic Autonomic
Reflexes that stimulate the skeletal muscles Somatic reflexes Reflexes that stimulate the skeletal muscles Autonomic reflexes Regulate activity of smooth muscle, heart, glands, saliva, pupil size, and BP
Reflex arc
Reflexes Many reflexes involve only spinal cord neurons and occur without brain involvement
Sympathetic Nervous System “Fight or flight” reaction Parasympathetic Nervous System “Rest and digest”