Chapter 44-The Nervous System Flashcards
Stimulus
Changes in the environment; all changes involve changes in energy
Sensory Receptors
detect stimulus
Motor effectors
respond to stimuli
The nervous system does what for an organism
allows organisms to detect changes and respond to environmental stimuli
Structure of Neurons
- Cell Body-enlarged part containing nucleus
- Dendrites-several short cytoplasmic extensions that receive stimuli
- Axon-usually 1, long extension that conducts impulses away from cell body
What do neurons do
produce the action potential
3 Types of Neurons
- Sensory Neurons
- Motor Neurons
- Interneurons
Sensory Neurons
(afferent neurons)
-carry impulses to CNS from sensory cells and organs
Motor Neurons
- Efferent Neurons
- carry impulses from CNS to effectors (muscles and glands)
Interneurons
- Association Neurons
- provide more complex reflexes and associative functions (learning and memory)
Central Nervous System
brain and spinal cord
-site of integration and higher processes
Peripheral Nervous System (PNS)
- Sensory and motor neurons;sensory cells
- somatic NS and Autonomic NS
- -sympathetic and parasympathetic NS
Somatic NS
branch of PNS
-stimulates skeletal muscles
Autonomic NS
branch of PNS
- stimulates smooth and cardiac muscles, as well as glands
- divided into the Sympathetic and Parasympathetic NS that counterbalance each other
Neuroglia
-Support cell of NS
-supports neurons both structurally and functionally (nourish, remove wastes, assist in condition)
-Schwann cells, oligodendrocytes
-
Schwann cells and oligodendrocytes
- Neuroglia
- produce myelin sheaths surrounding axons
- in CNS, myelinated axons form white matter
- dendrites/cell bodies form gray matter
- in PNS, myelinated axons are bundled to form nerves
Nerve impulse
the action potential, electrochemical in nature
- electric-movement of charge
- chemical-movement of ions
- along cell membranes, b/c of separation of ions across the cell membrane, there is a form of electrical potential energy called a membrane potential. measured in volts
The electrical potential energy difference in reference to the two sides of the neurons plasma membrane
Negative pole=cytoplasmic side
Positive pole=extracellular fluid side
Resting potential
when a neuron is not actively being stimulated=resting neuron
-resting potential is about -70 mV
2 main forces that act on ions in establishing the resting membrane potential
- electrical potential produced by unequal distribution of charges
- Concentration gradient produced by unequal concentrations of molecules form one side of the membrane to the other
what 3 things make the inside of the neuron more negative than the outside
- Sodium-potassium pump
- Ion leakage channels
- Movement of intracellular negative ions to inside of membrane
Sodium-Potassium pump
(+ outside)
- brings 2 K+ into cell for every three Na+ it pumps out
- creates significant concentration gradient
Ion Leakage channels
(+ outside)
-allow more K+ to diffuse out than Na+ to diffuse in
The resting potential-how does it work
sodium potassium pump creates significant concentration gradient
- concentration of K+ is much higher inside the cell so potassium diffuses out
- membrane not permeable to negative ions
- leads to buildup of positive charges outside and negative charges inside
2 types of changes to resting potential in neurons as a response to stimuli
- Graded potentials
- action potentials-nerve impulse
Graded Potentials
- Small transient changes in membrane potential due to activation of gated ion channels in response to a weak stimulus
- each gated channel is selective for a specific ion
- most are closed in the normal resting cell
- voltage regulated
Depolarization
makes the membrane potential more positive
Hyperpolarization
makes membrane potential more negative
Action Potentials
Result when depolarization reaches the threshold potential (-55 mV)
- Depolarizations bring a neuron further from the threshold
- Hyperpolarizations move the neuron further from the threshold
- caused by voltage-gated ion channels opening
- a wave of depolarization followed by a wave of repolarization
Voltage gated Na+ channels
- have activation gate and inactivation gate
- at rest, activation gate closed, inactivation gate open
- transient influx of Na+ causes membrane to depolarize
Voltage gated K+ channels
- single activation gate that is closed in the resting state
- K+ channel opens slowly
- Efflux of K+ repolarizes the membrane
Propagation of action potentials
- each action potential, in its rising phase, reflects a reversal in membrane polarity
- positive charges due to influx of Na+ can depolarize the adjacent region to threshold
- and so the next region produces its own action potential
- meanwhile, the previous region repolarizes back to the resting membrane potential
2 ways to increase velocity of conduction
- axon has a larger diameter
- axon is myelinated
synapses
intracellular junctions of the axons of one neuron with the dendrites of other neurons, with muscle cells, or with gland cells
Electrical synapses
Involve direct cytoplasmic connections between the two cells formed by gap junctions
-relatively rare in vertebrates
Chemical Synapses
- Have a synaptic cleft between the two cells
- end of presynaptic vesicles packed with neurotransmitters
Chemical Synapses (in depth)
action potential triggers influx of Ca2+
-synaptic vesicles fuse with cell membrane
-neurotransmitter is released by exocytosis
Diffuses to other side of cleft and binds to chemical-or ligand-gated receptor proteins
-produces graded potentials in the postsynaptic membrane
-neurotransmitter action is terminated by enzymatic cleavage or cellular uptake
Acetylcholine
Neurotransmitter (ACh)
- crosses the synapse between a motor neuron and a muscle fiber
- neuromuscular junction
- binds to receptor in the postsynaptic membrane
- causes ligand-gated ion channels to open
- produces a depolarization called an excitatory postsynaptic potential (EPSP)
- stimulates muscle contraction
What causes muscle relaxation
Acetylcholinesterase (ACHe)
Amino acids as Neurotransmitters
- Glutamate
2. Glycine and GABA
Glutamate
- Neurotransmitter, amino acid
- major excitatory neurotransmitter in the vertebrate CNS
Glycine and GABA
- Neurotransmitter, Amino Acid
- Inhibitory nerotransmitters
- open ligand-gated channels for Cl-
- produce a hyperpolarizatoin called an inhibitory postsynaptic potential (IPSP)
Biogenic amines
Neurotransmitters
- epinephrine and norepinephrine are responsible for “flight or fight” response
- Dopamine, used in areas of the brain that control body movements
- seratonin is involved in regulation of sleep
Three basic divisions of vertebrate brain
- Hindbrain, or rhombencephalon
- Midbrain, or mesencephalon
- Forebrain, or prosencephalon
Dominant brain feature in Vertebrates
forebrain
2 elements that compose forebrain
Diencephalon
-Thalamus-integration and relay center
-hypothalamus-participates in basic drives and emotions, controls pituitary gland, regulates body temp.
Telencephalon (end brain)
-devoted largely to associative activity
-called cerebrum in mammals (brain basically)
Corpus callosum
connects the right and left cerebral hemispheres
Divisions of the brain hemispheres
Frontal, parietal, temporal, and occipital lobes
Cerebral cortex
outer layer of the cerebrum
- contains about 10% of all neurons in brain
- highly convoluted
3 regions of cerebral cortex (and one more)
- Primary motor cortex-movement control
- Primary somatosensory cortex-sensory control
- Association cortex-higher mental functions
- Basal ganglia
- -aggregates of neuron cell bodies-gray matter
- -participate in the control of body movements
Thalamus
integrates visual, auditory and somatosensory information
Hypothalamus
integrates visceral activities, controls pituitary gland
Limbic system
- hypothalamus, hippocampus, and amygdala
- responsible for emotional responses
Left hemisphere
controls right side of body
-dominant in language
Right hemisphere
adept at spatial reasoning
-primarily involved in musical ability
Memory
short term memory is stored in form of transient neural excitations
- long term memory involves structural changes in neural connections
- hippocampus and amygdala involved in both parts
Alzheimers disease
- condition where memory and thought become dysfunctional
- 2 causes
1. nerve cells are killed from the outside in
2. nerve cells are killed form inside out
2 zones of spinal chord
- inner zone is gray matter, primarily consists of the cell bodies of interneurons, motor neurons, and neuroglia
- Outer zone is white matter, contains cables of sensory axons in the dorsal columns and motor axons in the ventral columns
Functions of Spinal Chord
- relays messages between the body and the brain
- also functions in relexes
- -knee jerk reaction is monosynaptic
- -most reflexes in vertebrates involve a single interneuron
The PNS
consists of nerves and ganglia
-function is to receive info from the environment, convey it to CNS, and to carry responses to effectors such as muscle cells
Nerves
bundles of axons bound by connective tissue
Ganglia
aggregates of neuron cell bodies
Sensory Neurons
- PNS
- axons enter the dorsal surface of the spinal cord and form dorsal root of spinal nerve
- cell bodies are grouped outside the spinal cord in dorsal root ganglia
Motor Neurons
- axons leave from the ventral surface and form ventral root of spinal nerve
- cell bodies are located in the spinal cord
Somatic nervous system
Somatic motor neurons stimulate the skeletal muscles to contract
- in response to conscious command or reflex actions
- antagonist of the muscle is inhibited by hyperpolarization (IPSPs) of spinal motor neurons
Autonomic Nervous system
Composed of the sympathetic and parasympathetic divisions, plus medulla oblongata. The para and sympathetic divisions work to contrast each other
- in both, efferent motor pathway has 3 neurons
- -Preganglionic neuron
- -Postganglionic neuron
Preganglionic neuron
- exits the CNS and synapses at an autonomic ganglion
- part of ANS
Postganglionic Neuron
exits the ganglion and regulates visceral effectors
-smooth or cardiac muscle or glands
Sympathetic Division
PNS, ANS
- preganglionic neurons originate in the thoracic and lumbar regions of spinal chord
- most axons synapse in two parallel chains of ganglia right outside the spinal cord
Parasympathetic Division
PNS, ANS
- preganglionic neurons originate in the brain and sacral regions of spinal cord
- axons terminate in ganglia near or even within internal organs
