Key terms
120 terms- Sensory (afferent) neuron§42.1
- Carries a signal from a receptor to the CNS
- Motor (efferent) neuron§42.1
- Carries a signal from the CNS out to a muscle or gland
- Interneuron (association neuron)§42.1
- Neuron entirely within the CNS that links other neurons
- Central nervous system (CNS)§42.1
- Brain plus spinal cord — the command center
- Peripheral nervous system (PNS)§42.1
- All sensory and motor neurons outside the brain and spinal cord
- Somatic nervous system§42.1
- Voluntary motor control of skeletal muscle
- Autonomic nervous system§42.1
- Involuntary control of smooth muscle, cardiac muscle, and glands
- Sympathetic division§42.1
- Autonomic division for fight or flight
- Parasympathetic division§42.1
- Autonomic division for rest and repose
- Cell body§42.1
- Enlarged neuron region holding the nucleus; integrates dendrite input
- Dendrite§42.1
- Branched extension that receives input and carries it toward the cell body
- Dendritic spine§42.1
- Small projection adding receiving surface area to a dendrite
- Axon§42.1
- The single output fiber carrying impulses away from the cell body
- Glial cells (neuroglia)§42.1
- Support cells; ~1/10 the size of neurons but ~10× more numerous
- Schwann cell§42.1
- PNS glial cell that wraps one axon segment in myelin
- Oligodendrocyte§42.1
- CNS glial cell that myelinates segments of several axons
- Myelin sheath§42.1
- Insulating wrap of compacted glial membrane around an axon
- Node of Ranvier§42.1
- Gap in the myelin sheath, every 1–2 µm, where action potentials fire
- White matter§42.1
- CNS regions of myelinated axons
- Gray matter§42.1
- CNS regions of unmyelinated cell bodies and dendrites
- Nerve§42.1
- PNS bundle of myelinated axons, like wires in a cable
- Astrocyte§42.1
- Star-shaped glial cell; helps build the blood–brain barrier, clears excess K⁺
- Blood–brain barrier§42.1
- Capillary barrier restricting what passes from blood into the CNS
- Ependymal cell§42.1
- Ciliated glial cell lining brain cavities; makes cerebrospinal fluid
- Microglia§42.1
- Immune glial cells acting as CNS macrophages
- Resting membrane potential§42.2
- Steady voltage of an unstimulated neuron; -40 to -90 mV, standard -70 mV
- Na⁺/K⁺ pump§42.2
- Active transporter moving 3 Na⁺ out for every 2 K⁺ in
- Leakage channel§42.2
- Ion channel that is always open; sets the resting potential
- Gated channel§42.2
- Ion channel that opens only in response to a stimulus
- Ligand-gated channel§42.2
- Channel opened by a chemical signal; produces graded potentials
- Voltage-gated channel§42.2
- Channel opened by a change in membrane potential; produces action potentials
- Equilibrium potential§42.2
- Voltage at which diffusional and electrical forces on one ion balance
- Nernst equation§42.2
- E_K = 58 mV · log([K⁺]out/[K⁺]in); computes one ion’s equilibrium potential
- Graded potential§42.2
- Small, stimulus-proportional, local change in potential that fades with distance
- Depolarization§42.2
- Membrane potential becomes less negative (e.g. -70 → -65 mV)
- Hyperpolarization§42.2
- Membrane potential becomes more negative (e.g. -70 → -75 mV)
- Repolarization§42.2
- Return toward the resting potential after depolarization, driven by K⁺ efflux
- Summation§42.2
- Combining of graded potentials to amplify or cancel each other
- Threshold§42.2
- Minimum depolarization (~-55 mV) that opens voltage-gated Na⁺ channels
- Action potential§42.2
- All-or-none spike from -70 mV to about +35 to +40 mV, lasting ~1 ms
- Undershoot§42.2
- Brief hyperpolarization after repolarization because K⁺ channels close slowly
- Absolute refractory period§42.2
- Interval when Na⁺ channels are inactivated and the cell cannot fire at all
- Relative refractory period§42.2
- Interval when the cell can fire, but only a smaller action potential
- Saltatory conduction§42.2
- Impulse jumping node to node along a myelinated axon; much faster
- Giant axon§42.2
- Very large-diameter invertebrate axon (squid) giving speed without myelin
- Synapse§42.3
- Junction where a neuron communicates with another cell
- Presynaptic / postsynaptic cell§42.3
- Sender and receiver across a synapse
- Electrical synapse§42.3
- Gap-junction connection passing potential changes directly and fast
- Chemical synapse§42.3
- Junction using a chemical messenger across a cleft; most vertebrate synapses
- Synaptic cleft§42.3
- Narrow gap between pre- and postsynaptic cells, visible only by electron microscope
- Synaptic vesicle§42.3
- Axon terminal sac storing neurotransmitter for exocytosis
- Neurotransmitter§42.3
- Chemical released by the presynaptic cell to affect the postsynaptic cell
- Neuromuscular junction§42.3
- Chemical synapse between a motor neuron and a muscle fiber
- Acetylcholine (ACh)§42.3
- Transmitter at the neuromuscular junction and many neuron-to-neuron synapses
- Acetylcholinesterase (AChE)§42.3
- Extremely fast enzyme that clears ACh by cleaving it in the cleft
- Glutamate§42.3
- Major excitatory neurotransmitter of the vertebrate CNS
- GABA / glycine§42.3
- Inhibitory transmitters that open Cl⁻ channels and hyperpolarize the membrane
- Catecholamine§42.3
- Tyrosine-derived biogenic amine: epinephrine, norepinephrine, dopamine
- Dopamine§42.3
- Movement-related transmitter; loss causes Parkinson, excess linked to schizophrenia
- Serotonin§42.3
- Tryptophan-derived amine regulating sleep and mood; target of SSRIs
- Neuromodulator§42.3
- Neuropeptide with subtler, longer-term postsynaptic effects
- Substance P§42.3
- Neuropeptide released in the CNS by pain-sensing sensory neurons
- Endogenous opiates§42.3
- Enkephalins and endorphins, which block pain via the opiate receptors
- Nitric oxide (NO)§42.3
- Gaseous transmitter made from arginine on demand; cannot be stored in vesicles
- EPSP§42.3
- Excitatory postsynaptic potential — a depolarization toward threshold
- IPSP§42.3
- Inhibitory postsynaptic potential — a hyperpolarization away from threshold
- Synaptic integration§42.3
- Summing EPSPs and IPSPs at the cell body to decide whether to fire
- Spatial summation§42.3
- EPSPs from many different synapses adding together at one time
- Temporal summation§42.3
- Repeated EPSPs from one synapse adding within about 15 ms
- Habituation§42.3
- Loss of responsiveness after prolonged constant stimulation
- Tolerance§42.3
- Need for more drug as the postsynaptic cell down-regulates its receptors
- Nerve net§42.4
- Diffuse web of neurons in cnidarians with no central control
- Tract§42.4
- Bundle of axons forming an information highway inside the CNS
- Hindbrain (rhombencephalon)§42.4
- Cerebellum, pons, and medulla oblongata; coordinates motor reflexes
- Midbrain (mesencephalon)§42.4
- Contains the optic tectum; reflexes involving eyes and ears
- Forebrain (prosencephalon)§42.4
- Diencephalon plus telencephalon; dominant in later vertebrates
- Cerebellum§42.4
- Hindbrain region coordinating movement, limb position, and balance
- Medulla oblongata§42.4
- Hindbrain region for autonomic functions and sensory nuclei
- Diencephalon§42.4
- Thalamus plus hypothalamus
- Thalamus§42.4
- Primary sensory integration and relay station to the cerebral lobes
- Hypothalamus§42.4
- Regulates temperature, hunger, thirst, emotion; controls the pituitary
- Telencephalon / cerebrum§42.4
- Front forebrain devoted to association, correlation, and learning
- Corpus callosum§42.4
- Axon tract connecting the two cerebral hemispheres
- Contralateral§42.4
- On the opposite side of the body from the controlling hemisphere
- Cerebral cortex§42.4
- Few-mm gray-matter surface layer with >10 billion neurons
- Gyrus / sulcus§42.4
- A surface fold and a surface groove of the brain
- Primary motor cortex§42.4
- Frontal lobe strip controlling voluntary movement, mapped by body part
- Primary somatosensory cortex§42.4
- Parietal lobe strip receiving skin and muscle sensation, mapped by body part
- Association cortex§42.4
- Non-motor, non-sensory cortex for higher mental activity; ~95% in humans
- Basal nuclei§42.4
- Gray-matter islands deep in cerebral white matter that help control movement
- Limbic system§42.4
- Hippocampus, amygdala, and hypothalamus — emotion and memory
- Hippocampus§42.4
- Limbic structure for forming and consolidating memories
- Reticular activating system (RAS)§42.4
- Brainstem network controlling alertness, consciousness, and sleep–wake state
- EEG§42.4
- Recording of brain electrical activity; alpha, beta, theta, delta waves
- Lateralization§42.4
- Specialization of the two hemispheres for different functions
- Broca’s area§42.4
- Frontal lobe area generating the motor output of speech
- Wernicke’s area§42.4
- Parietal lobe area for language comprehension; damage gives word salad
- Aphasia§42.4
- Language disorder caused by damage to a language area
- Prosopagnosia§42.4
- Inability to recognize faces, from nondominant inferior temporal damage
- Long-term potentiation (LTP)§42.4
- Synapse strengthened by AMPA receptor insertion after strong NMDA activation
- Long-term depression (LTD)§42.4
- Synapse weakened by AMPA receptor removal via calcineurin
- NMDA receptor§42.4
- Glutamate receptor needing both ligand binding and depolarization (Mg²⁺ block removal)
- Beta-amyloid / tau§42.4
- Alzheimer suspects — external plaques and internal neurofibrillary tangles
- Meninges§42.4
- Protective membrane layers covering the brain and spinal cord
- Reflex§42.4
- Fast, involuntary muscle response processed at the spinal cord
- Monosynaptic reflex arc§42.4
- Reflex with one synapse, sensory straight to motor (knee-jerk)
- Cutaneous reflex§42.4
- Skin reflex routed through one or more interneurons
- Dorsal root§42.5
- Sensory branch of a spinal nerve entering the cord dorsally
- Ventral root§42.5
- Motor branch of a spinal nerve leaving the cord ventrally
- Dorsal root ganglion§42.5
- Cluster of sensory neuron cell bodies just outside the spinal cord
- Preganglionic neuron§42.5
- First autonomic motor neuron; CNS cell body, always releases ACh
- Postganglionic neuron§42.5
- Second autonomic motor neuron; ganglion cell body to the effector organ
- Nicotinic receptor§42.5
- ACh receptor on skeletal muscle that opens directly as a Na⁺ channel
- Muscarinic receptor§42.5
- G-protein-linked ACh receptor; opens heart K⁺ channels and slows the beat
- G protein§42.5
- Membrane protein activated by a receptor that then activates an effector protein
- Sympathetic chain§42.5
- Paired ganglion chains beside the cord holding sympathetic postganglionic cell bodies
- Adrenal medulla§42.5
- Inner adrenal region secreting epinephrine when sympathetic fibers fire
- Cranial nerve§42.5
- One of 12 paired nerves arising from the underside of the brain, I–XII
- Vagus nerve (X)§42.5
- Cranial nerve reaching chest and abdominal organs; central to homeostasis
- Mixed nerve§42.5
- Nerve carrying both sensory and motor fibers