Nervous system Flashcards
3 functions of NS
- Sensory input: information gathered by sensory receptors about internal and external changes
- integration: interpretation of sensory input
- motor output: activation of effector organs (muscles + glands) produces a response
2 divisions of NS
CNS (Central nervous system)
- brain and spinal cord
- command center
PNS (Peripheral nervous system)
- paired spinal + cranial nerves carry messages to and from CNS
- 2 directions
2 types of PNS
- Sensory (afferent) division (to the brain):
- somatic afferent fibers - convey impulses from skin, skeletal muscles, and joints
- visceral afferent fibers - convey impulses from visceral organs - motor (efferent) division (away from brain):
- transmits impulses from CNS to effector organs (muscles/glands)
Motor divisions of PNS
- Somatic voluntary nervous system
- conscious control of skeletal muscles - Autonomic involuntary NS (ANS)
- regulates smooth, cardiac muscles, and glands
- sympathetic + parasympathetic
Histology of Nervous TIssue
2 cell types
1. Neurons: excitable cells that transmit electrical signals
2. Neuroglia (glial cells) - supporting cells:
- astrocytes: support
- Microglial: defensive -> immune surveillance
- ependymal: moves/create CSF
- oligodendrocytes: produces myelin -> insulation
- schwann cells (PNS): produces myelin -> insulation
Schwann cells
- surround peripheral nerve fibers + form myelin sheaths
- vital to regeneration of damaged peripheral nerve fibers
Nerve cell body
- biosynthetic center of a neuron
- rough ER: makes neurotransmitters
- axon hillock: cone-shaped area from which axon arises
- clusters of cell bodies are called Nuclei (CNS) and Ganglia (PNS)
Nerve cell processes
- dendrites (toward cell body)
- axons (generates impulse away)
bundles of processes are called
- tracts: CNS
- nerves: PNS
White + Gray matter
white matter
- dense collections of myelinated fibers (tracts)
gray matter
- mostly neuron cell bodies and unmyelinated fibers
Functional classification of neurons (3)
- Sensory: transmit impulses from sensory receptors toward CNS
- almost all are UNIPOLAR (one projection) - Motor: carry impulses from CNS to effectors
- MULTIPOLAR - Interneurons (association neurons): shuttle signals through CNS pathways; most are entirely within CNS
- 99% of body’s neurons
- lie bw motor and sensory neurons
- MULTIPOLAR
- bipolar = RARE
Resting membrane potential
- potential difference across membrane of a resting cell is approx. 70 mV in neurons (inside of membrane is neg charged relative to outside)
- generated by diff. in ionic makeup of ICF + ECF and differential permeability of the plasma membrane
- diff in ionic make up
(outside cell has HIGH Na+, INSIDE has HIGH K+ and neg. charged proteins)
Membrane potentials that acts as signals
Membrane potential changed when:
- concentrations of ions across membrane change
- permeability of membrane to ions changes
- changes in membrane potential are signals used to receive + send info
2 types
- graded potential: local signals (dendrites)
- action potential: long distance signals (axons)
Changes in membrane potential
- Depolarization
- reduction in membrane potential (toward zero)
- inside of membrane becomes LESS NEG than resting potential - Graded potentials
- short, localized changed in membrane potential
- depolarizations (excite) or hyperpolarizations (inhibit)
- spreads as local currents - Action Potentials
- brief reversal of membrane potential with 100 mV
- muscle cells and axons of neurons
- doesn’t decrease in magnitude over distance
- long-distance neural communication
Generation of AP
Resting state
- leakage channels of K+ and Na+ open
- all gated Na+ and K+ are closed
Depolarization
- open voltage gated Na+
Repolarization
- slow voltage sensitive K+ gates open
- K+ exits cell and internal negativity restored
Hyperpolarization
- some K+ channels remain open, allowing excessive K+ efflux
Stimulus Intensity coding
- all AP are alike and independent of stimulus intensity
- strong stimuli = occur frequently (#of impulses per second or freq of APs)
- CNS determines stimulus intensity by freq of impulses (HIGH freq = STRONGER stimulus)
Absolute + Relative Refractory period
Absolute: time from opening of Na+ channels until resetting of channels
- Another AP CANT fire during the period
Relative: repolarization occurring
- threshold for AP generation is elevated
- exceptionally strong stimulus may generate an AP
Synapse
Junction that mediates info transfer from one neuron:
- to another neuron, or effector cell (NMJ)
- release of neurotransmitter
-has a presynaptic neuron and postsynaptic neuron
Chemical synpases
- specialized for release and reception of neurotransmitters
- typically composed of 2 parts: axon terminal of presynaptic neuron, which contains the vesicles
Termination fo neurotransmitter effects
within a few milliseconds, neurotransmitter effect is terminated
- degradation of enzymes
- reuptake via astrocytes or axon terminal
- diffusion away from synaptic cleft
Postsynaptic potentials
graded potentials strength determines by:
- amt of neurotransmitter released
- time neurotransmitter is in area
types of postsynaptic potentials
1. EPSP: excitatory postsynaptic potentials
2. IPSP: inhibitory postsynaptic potentials
Types of summation
- Spatial: several neurons firing ALL AT ONCE
- Temporal: one neuron fires MANY TIMES
Neurotransmitters
- most neurons make 2/more neurotransmitters
Biogenic amines include:
- catecholamines: dopamine, norepinephrine, epinephrine
- indolamines: serotonin, histamine
Acetylcholine:
- released at neuromuscular junctions and some ANS neurons
- major neurotransmitter that controls muscle action
Dopamine
Pleasure/reward
- our brains are wired to reward us with pleasure when we engage in behavior necessary for species survival (food/reproduction)
Drugs of abuse (crack/cocaine)
- block re-update of dopamine
- allows body to feel its effects over a prolonged period
- with continued use, body stops making dopamine
- produces depression + cravings for the drug
