Biology, Nervous system

Raven Biology 13th edition, CH42

Figure 42.2 Types of Neurons, the diagram shows the three types of neurons and their functions sensory neurons

afferent carry impulses to CNS

Figure 42.2 Types of Neurons, the diagram shows the three types of neurons and their functions motor neurons

efferent carry impulses from CNS to effectors

Figure 42.2 Types of Neurons, the diagram shows the three types of neurons and their functions interneurons

association neurons provide more complex reflexes and associative functions (learning and memory)

Components of a Neuron, neurons have the same basic structure

cell body (enlarged part containing nucleus), dendrites (short cytoplasmic extensions that receive stimuli), and axon (single long extension that conducts impulses away from cell body)

Supportive Cells, Neuroglia support neurons both structurally and functionally

Schwann cells (PNS) and oligodendrocytes (CNS) produce myelin sheaths surrounding axons

Supportive Cells, In the CNS, myelinated axons form white matter

dendrites and cell bodies form gray matter; in the PNS, myelinated axons are bundled to form nerves

Figure 42.3b Myelin Sheath Formation, the diagram shows the formation of the myelin sheath around a peripheral axon

Schwann cells wrap around the axon multiple times, creating concentric layers of membrane that insulate the axon and increase conduction velocity

Gated Channels, Chemically-gated or ligand-gated channels

ligands are chemical signals (hormones or neurotransmitters) that induce opening and cause changes in cell membrane permeability

Figure 42.7 Graded Potentials, the diagram shows depolarization and hyperpolarization graded potentials

depolarization makes the membrane potential more positive; hyperpolarization makes it more negative; these small changes result in graded potentials whose size depends on stimulus strength

Phases of an Action Potential, the action potential has three phases

rising, falling, and undershoot; action potentials are always separate, all-or-none events with the same amplitude; intensity of a stimulus is coded by frequency, not amplitude

Nerve Impulse Propagation, propagation of action potentials occurs as each action potential reflects a reversal in membrane polarity

positive charges due to Na+ influx depolarize the adjacent region to threshold, so the next region produces its own action potential while the previous region repolarizes

Chemical Synapses, action potential triggers influx of Ca2+

synaptic vesicles fuse with cell membrane; neurotransmitter is released by exocytosis; diffuses and binds to ligand-gated receptor proteins; produces graded potentials; neurotransmitter action terminated by enzymatic digestion or cellular uptake

Acetylcholine, Acetylcholine (ACh) crosses the synapse between a motor neuron and a muscle fiber at the neuromuscular junction

binds to receptor in postsynaptic membrane causing ligand-gated channels to open, producing EPSP that stimulates muscle contraction

Acetylcholine, Acetylcholinesterase (AChE) degrades ACh

causes muscle relaxation

Neurotransmitters: Amino Acids, Glutamate is the major excitatory neurotransmitter in the vertebrate CNS

glycine and GABA (γ-aminobutyric acid) are inhibitory neurotransmitters that open ligand-gated Cl- channels, producing hyperpolarization called IPSP

Neurotransmitters: Biogenic Amines, Epinephrine (adrenaline) and norepinephrine are responsible for the "fight or flight" response

dopamine is used in areas of the brain that control body movements; serotonin is involved in regulation of sleep

Neurotransmitters: Neuropeptides, Substance P is released from sensory neurons activated by painful stimuli

intensity of pain perception depends on enkephalins and endorphins; nitric oxide (NO) is a gas produced from arginine that causes smooth muscle relaxation

Synaptic Integration and Threshold Voltage, two ways the membrane can reach threshold voltage

spatial summation (many different dendrites produce EPSPs) and temporal summation (one dendrite produces repeated EPSPs)

Drug Addiction, Habituation occurs when prolonged exposure to a stimulus causes cells to lose ability to respond

cell decreases number of receptors due to excess neurotransmitters; more drug needed for same effect in long-term use

Drug Addiction: Cocaine, Cocaine affects neurons in the brain's "pleasure pathways" (limbic system)

binds dopamine transporters and prevents reuptake of dopamine; dopamine survives longer in synapse and fires pleasure pathways more frequently

Drug Addiction: Nicotine, Nicotine binds directly to a specific receptor on postsynaptic neurons

binds to a receptor for acetylcholine; brain adjusts to prolonged exposure by making fewer receptors and altering activation patterns

Table 42.4 Subdivisions of the Central Nervous System, Spinal Cord

spinal reflexes; relays sensory and motor information

Table 42.4 Subdivisions of the Central Nervous System, Hindbrain (rhombencephalon) Medulla oblongata

sensory nuclei; reticular-activating system; autonomic functions

Table 42.4 Subdivisions of the Central Nervous System, Hindbrain (rhombencephalon) Pons

reticular-activating system; autonomic functions

Table 42.4 Subdivisions of the Central Nervous System, Hindbrain (rhombencephalon) Cerebellum

coordination of movements; balance

Table 42.4 Subdivisions of the Central Nervous System, Midbrain (mesencephalon)

reflexes involving eyes and ears

Table 42.4 Subdivisions of the Central Nervous System, Forebrain (prosencephalon) Diencephalon Thalamus

relay station for ascending sensory and descending motor tracts; autonomic functions

Table 42.4 Subdivisions of the Central Nervous System, Forebrain Diencephalon Hypothalamus

autonomic functions; neuroendocrine control

Table 42.4 Subdivisions of the Central Nervous System, Forebrain Telencephalon (cerebrum) Basal nuclei

motor control

Table 42.4 Subdivisions of the Central Nervous System, Forebrain Telencephalon Corpus callosum

connects and relays information between the two hemispheres

Table 42.4 Subdivisions of the Central Nervous System, Forebrain Telencephalon Hippocampus

memory; emotion (limbic system)

Table 42.4 Subdivisions of the Central Nervous System, Forebrain Telencephalon Cerebral cortex

higher cognitive functions; integrates and interprets sensory information; organizes motor output

Cerebrum, the increase in brain size in mammals reflects great enlargement of the cerebrum

split into right and left cerebral hemispheres connected by corpus callosum; each hemisphere receives sensory input from opposite side; divided into frontal, parietal, temporal, and occipital lobes

Cerebral Cortex, primary motor cortex controls movement

primary somatosensory cortex controls sensation; association cortex handles higher mental functions; basal nuclei (gray matter aggregates) participate in body movement control

Other Brain Structures, Thalamus integrates visual, auditory, and somatosensory information

Hypothalamus integrates visceral activities and controls pituitary gland; Limbic system (hypothalamus, hippocampus, amygdala) responsible for emotional responses

Complex Functions of the Brain: Sleep and Arousal, one section of reticular formation is the reticular-activating system

controls consciousness and alertness; brain state monitored by electroencephalogram (EEG) which records electrical activity

Complex Functions of the Brain: Language, left hemisphere is "dominant" hemisphere for language

different regions control various language activities; left hemisphere adept at sequential reasoning; right hemisphere adept at spatial reasoning and musical ability

Complex Functions of the Brain: Memory, short-term memory stored as transient neural excitations

long-term memory involves structural changes in neural connections; hippocampus and amygdala (temporal lobes) involved in short-term memory and consolidation into long-term memory

Synaptic Plasticity, cellular basis of learning and memory involves long-term changes in synaptic connection strength

two examples: long-term potentiation (LTP) and long-term depression (LTD)

Alzheimer Disease, condition where memory and thought become dysfunctional

two causes: nerve cells killed from outside in by external protein β-amyloid; nerve cells killed from inside out by internal proteins tau (τ)

Spinal Cord, cable of neurons extending from brain down through backbone

enclosed and protected by vertebral column and meninges

Composition of the Peripheral Nervous System, consists of nerves and ganglia

nerves are bundles of axons bound by connective tissue; ganglia are aggregates of neuron cell bodies; function is to receive info, convey to CNS, and carry responses to effectors

Table 42.5 Comparison of Somatic and Autonomic Nervous Systems, Somatic NS effectors are skeletal muscle

effect on motor nerves is excitation; innervation of effector cells is always single; number of sequential neurons is one; neurotransmitter is acetylcholine

Table 42.5 Comparison of Somatic and Autonomic Nervous Systems, Autonomic NS effectors are cardiac muscle, smooth muscle, GI tract, blood vessels, airways, exocrine glands

effect on motor nerves is excitation or inhibition; innervation is typically dual; number of sequential neurons is two; neurotransmitters are acetylcholine and norepinephrine

Divisions of the Autonomic Nervous System, Sympathetic division preganglionic neurons originate in thoracic and lumbar regions

most axons synapse in two parallel chains of ganglia right outside the spinal cord

Divisions of the Autonomic Nervous System, Parasympathetic division preganglionic neurons originate in brain and sacral regions

axons terminate in ganglia near or even within internal organs

G Proteins, mediate cell responses to autonomic signals

activate target cells

Cranial Nerves, twelve pairs of cranial nerves arise from underside of brain

carry sensory neurons for special and general senses as well as somatic and autonomic motor neurons

Table 42.7 Cranial Nerves and Their Functions, Olfactory

sense of smell

Table 42.7 Cranial Nerves and Their Functions, Optic

vision

Table 42.7 Cranial Nerves and Their Functions, Oculomotor

motor control of some eye muscles and eyelid

Table 42.7 Cranial Nerves and Their Functions, Trochlear

motor control of some eye muscles

Table 42.7 Cranial Nerves and Their Functions, Trigeminal

chewing muscles and some facial sensation

Table 42.7 Cranial Nerves and Their Functions, Abducent

motor control of some eye muscles

Table 42.7 Cranial Nerves and Their Functions, Facial

motor control of facial muscles, salivation, taste, and cutaneous sensations

Table 42.7 Cranial Nerves and Their Functions, Acoustic

equilibration, static sense, and hearing

Table 42.7 Cranial Nerves and Their Functions, Glossopharyngeal

salivation, sensations of skin, taste, and viscera

Table 42.7 Cranial Nerves and Their Functions, Vagus

motor control of the heart and viscera, sensation from thorax, pharynx, and abdominal viscera

Table 42.7 Cranial Nerves and Their Functions, Accessory

motor impulses to the pharynx and shoulder

Table 42.7 Cranial Nerves and Their Functions, Hypoglossal

motor control of the tongue, some skeletal muscles, some viscera, sensation from skin and viscer