Embedded Files
Nervous Systems Organization of the Nervous System- Central nervous system (CNS) = brain + spinal cord- Peripheral nervous system (PNS) = nerves throughout body§ Sensory receptors: collect info§ Sensory neurons: body à CNS§ Motor neurons: CNS à body (muscles, glands)§ Interneurons: connect sensory & motor neurons- Nerves = bundles of neurons§ Contains motor neurons +/or sensory neurons Functional Organization of the Nervous SystemNervous System – divided into sensory (afferent) and motor (efferent) Sensory division – transmits information from periphery to the CNS, contains receptors -somatic sensory: receives sensory information from skin, fascia, joints, skeletal muscles, special censes -visceral sensory: receives sensory information from viscera Motor division – transmits information from CNS to the rest of the body, sends motor information to effectors -somatic motor: voluntary nervous system – innervates skeletal muscle -autonomic motor: involuntary nervous system – innervates cardiac muscle, smooth muscle, glands how central and peripheral nervous system are linked:Sensory input from sensor (like eye) brought to CNS via PNS à integration into the CNS à motor output to effector (like leg) brought to effector from CNS via PNS Peripheral Nervous SystemPeripheral Nervous System: somatic and autonomicsomatic: voluntary nervous system – innervates skeletal muscleautonomic: involuntary nervous system – sympathetic, parasympathetic, enteric parasympathetic action on target organs: constricts pupils of the eyes, stimulates salivary gland secretion, constricts bronchi in lungs, slows heart, stimulates activity of stomach and intestines, stimulates activity of pancreas, stimulates gallbladder, promotes erection of genitals sympathetic action on target organs: dialates pupils, inhibits salivary glands, relaxes bronchi in lungs, accelerates heart, inhibits activity of pancreas, stimulates glucose release from liver, inhibits gallbladder, stimulates adrenal medulla, inhibits emptying of bladder, promotes ejaculation and vaginal contractions. Neuron = dendrite + cell body + axon- cell body: contains nucleus & organelles- dendrites: receive incoming messages- axons: transmit messages away to other cells- myelin sheath: fatty insulation covering axon, speeds up nerve impulses- synapse: junction between 2 neurons- neurotransmitter: chemical messengers sent across synapse- Glia: cells that support neurons§ Eg. Schwann cells (forms myelin sheath) Membrane Potential: difference in electrical charge across cell membrane The Na+/K+ pump (using ATP) maintains a negative potential inside the neuron.Action potentials (nerve impulses) are the signals conducted by axons- Resting potential: membrane potential at rest; polarized§ Na+ outside, K+ inside cell§ Voltage-gated Na+ channel = CLOSED- Nerve impulse: stimulus causes a change in membrane potential§ Action potential: neuron membrane depolarizes§ All-or-nothing response Sodium channels open à sodium enters the cell à potassium channels open à potassium leaves the cell à conduction of an action potential Saltatory conduction: nerve impulse jumps between nodes of Ranvier (unmyelinated gaps) à speeds up impulse Saltatory conduction speed: 120 m/sec Cell communication: neurotransmitter released at synapsesAxon (presynaptic cell) à Dendrite (postsynaptic cell) Neurotransmitters- Chemicals released from vesicles by exocytosis into synaptic cleft- Diffuse across synapse- Bind to receptors on neurons, muscle cells, or gland cells- Broken down by enzymes or taken back up into surrounding cells- Types of neurotransmitters:§ Excitatory: speed up impulses by causing depolarization of postsynaptic membrane§ Inhibitory: slow impulses by causing hyperpolarization of postsynaptic membrane Examples of Neurotransmitters- Acetylcholine (ACh): stimulates muscles, memory formation, learning- Epinephrine: (adrenaline) fight-or-flight- Norepinephrine: fight-or-flight- Dopamine: reward, pleasure (“high”)§ Loss of dopamine à Parkinson’s Disease- Serotonin: well-being, happiness§ Low levels à Depression- GABA: inhibitory NT§ Affected by alcohol Nervous System Disorders- LSD/mescaline – bind to serotonin and dopamine receptors à hallucinations- Prozac – enhances effect of serotonin by inhibiting uptake after release- Morphine, heroin – bind to endorphin receptors à decrease pain perception- Alzheimer’s Disease (AD) – develop senile plaques, shrinkage of brain tissue Reflexes- Simple, automatic response to a stimulus- Conscious thought not required- Reflex arc:1. Stimulus detected by receptor2. Sensory neuron3. Interneuron (spinal cord or brain stem)4. Motor neuron5. Response by effector organ (muscles, glands) Vertebrate brain is regionally specializedMajor Regions: forebrain, midbrain, hindbrain
Gray matter: neuron cell bodies, unmyelinated axonsWhite matter: fatty, myelinated axons
Google Sites
Report abuse