Unit 7 The Nervous System I. Functions of the Nervous System Monitors body's internal and external enviornments Integrates sensory information Coordinates voluntary & involuntary responses of many other organ systems
II. Divisions of the Nervous System A. Structural Divisions > CNS: Central Nervous System» Brain & Spinal Cord > PNS: Peripheral Nervous System» Cranial (12 pairs) & Spinal (31 pairs) nerves II. Divisions cont. B. Functional Divisions > Somatic: Connects CNS to skin & skeletal muscles» voluntary > Autonomic: Connects CNS to vicera, smooth & cardiac muscle, and certain glands» involuntary 1. Sympathetic: "fight-or-flight" system > prepares body for physical activity 2. Parasympathetic: "resting & digesting" system > promotes normal digestion, elimination & conserving body energy
Meyers' A&P February 15, 2016 III. Cells of the Nervous System A. Two Types 1. Neurons Receive stimuli and conduct action potentials 2. Neuroglia (non-neural) Protects neurons and perform other functions
III. Cells of the Nervous System B. Neuron Structure Cell Body Axon :Carry A.P. away from cell body Nucleus Dendrites :Carry A.P. towards cell body Axon Terminals III. Cells of the Nervous System C. Structural Variation in Neurons Multipolar Many fibers (dendrites) to cell body, only 1 axon carrying impulse away Axon Unipolar Single fiber from cell body, dendrite connects to peripheral and axon to the brain or spinal cord Bipolar Axon 2 fibers, axon & dendrite (eyes, nose, ears) Axon
III. Cells of the Nervous System D. Functional Variation in Neurons Sensory Neurons (afferent neurons) Carry AP's from peripheral receptors to CNS Interneurons (association neurons) Lie within CNS, distribute sensory info & coordinate response Motor Neurons (efferent neurons) Carry AP's from CNS to effectors
- Interneuron - Association Neuron - Motor Neuron - Sensory Neuron - Afferent Neuron - Efferent Neuron Effector Receptor III. Cells of the Nervous System E. Neuroglia Cells (not neurons) (Glial Cells) Astrocyte: provide support & regulate what leaves blood and reaches neurons Ependymal Cells: secrete & help circulate CSF CSF: Cerebrospinal Fluid Microglia: Similar to macrophages; destroy bacteria Oligodendrocyte: Form myelin sheath of axons in CNS Schwann Cell: Forms myelin sheath of axons outside CNS Satellite Cell: Act as cushioning for cells outside CNS Increased Lipids
IV. Conduction of a Nerve Impulse 1. Threshold stimulus recieved 2. Na + channels in a local region of membrane open 3. Na + diffuses into cell, depolarizing membrane 4. K + channels in the membrane open 5. K + diffuses out of cell, repolarizing membrane 6. Results in Action Potential, bioelectric current, which stimulates adjacent portions of membrane 7. Wave of action potential travels length of neuron as nerve impulse. All or None Law- once a threshold stimulus is reached; a nerve impulse is conducted...all impulses are the same strength. A greater intensity of stimulus does NOT produce a stronger impulse, but rather produces more impulses per second.
Meyers' A&P February 15, 2016 V. Neuron to Neuron Communication A. Synapse > Connection of one neuron to the next > Allows communication from Pre-synaptic neuron to the postsynaptic neuron > Uses various neurotransmitters to pass information > Action potential from 1st neuron triggers A.P. in 2nd
VI. Anatomy of a Reflex Arc 1. Receptor: detects/receives signal + Stimuli triggers Na channels to open if enough Na+ rushes in (threshold), An A.P. is Generated 2. Sensory Neuron: carries impulse to CNS (Afferent Neurons) 3. Interneuron: found in CNS, connects sensory - motor (Association Neurons) 4. Motor Neuron: from CNS to the effector (Efferent Neurons) 5. Effector: muscle, gland or organ that carries out response