Biology 30 13.1-13.4

What are the two main divisions of the peripheral nervous system and how do they differ?

Autonomic (involuntary; regulates internal environment) and sensory–somatic (external environment; senses stimuli and controls voluntary movements).

What does the autonomic nervous system regulate and how is it controlled?

Regulates the internal environment (e.g., heart rate, digestion, blood pressure) automatically, without conscious control.

What is the sensory–somatic division responsible for?

Sensing external environmental stimuli (light, touch, sound, taste) and controlling voluntary motor actions via motor neurons.

In the peripheral nervous system, which direction do sensory and motor neurons travel with respect to the CNS?

Sensory neurons enter the CNS (toward the brain/spinal cord); motor neurons exit the CNS (toward muscles).

What are the two divisions of the autonomic nervous system and their primary roles?

Sympathetic (fight or flight) and parasympathetic (rest and digest).

What are the main consequences of sympathetic activation on heart rate and digestion?

Heart rate increases; peristalsis/digestion decreases (digestion slows).

What are the main consequences of parasympathetic activation on heart rate and digestion?

Heart rate decreases; peristalsis increases (digestion active).

What happens to pupil size during sympathetic activation?

Pupil dilates (mydriasis) to allow more light in.

What happens to pupil size during parasympathetic activation?

Pupil constricts (miosis) to reduce light entry.

What happens to the bladder sphincter during sympathetic vs parasympathetic activation?

Sympathetic: sphincter constricts to prevent urination; Parasympathetic: sphincter relaxes to allow urination.

Which hormone is released by the adrenal glands during sympathetic activation?

Epinephrine (adrenaline).

What is peristalsis and how is it affected by the autonomic nervous system?

Rhythmic contractions of the digestive tract; increased by parasympathetic activation.

Which brain structure is primarily associated with autonomic control according to the notes?

Medulla oblongata (brainstem; noted as number four in the diagram).

What is biofeedback?

Conscious effort to control normally involuntary autonomic responses; activity is thought to originate in the cerebrum.

In anaphylaxis, what changes occur in blood pressure and airway bronchioles?

Blood pressure decreases and bronchioles constrict (bronchoconstriction), reducing oxygen delivery.

How do sympathetic and parasympathetic divisions affect glucose in the blood?

Sympathetic increases glucose release into the blood; parasympathetic promotes glucose storage (decreases blood glucose).

How are sensory signals and reflex arcs related in the peripheral nervous system?

Reflex arcs bypass the brain but still use sensory–somatic peripheral neurons; sensory information enters the CNS and a rapid motor response exits.

What does the term 'somatic' mean in sensory–somatic?

Body; related to sensing and voluntary motor control throughout the body.

What does the term 'autonomic' mean and what does it regulate?

Relates to the internal environment; regulates involuntary functions such as heart rate, digestion, respiration, and kidneys.

Which division is associated with erection and ejaculation, and which is which?

Parasympathetic promotes erection; Sympathetic promotes ejaculation.

What does the CNS stand for and what structures does it include?

Central nervous system; includes the brain and spinal cord.

What are the two main divisions of the nervous system?

Central nervous system (CNS) and peripheral nervous system (PNS).

What protects the brain and spinal cord?

The skull and vertebrae (backbone) plus protective coverings (meninges) and cerebrospinal fluid (CSF).

What are the meninges?

Protective wrapping layers around the brain (and spinal cord).

What is cerebrospinal fluid (CSF) and what does it do?

Fluid around the brain and spinal cord; cushions (shock absorber) and transports nutrients, wastes, and oxygen.

What is the spinal cord's function in the nervous system?

Carries sensory information from the peripheral nervous system to the brain; a fast communication highway between PNS and brain.

Backbone vs spinal cord: what is protected by each?

Backbone (vertebral column) is bone that protects the spinal cord and provides structure; the spinal cord is the nerve bundle running inside it.

Gray matter vs white matter in the CNS

Gray matter contains neuron cell bodies; white matter contains myelinated axons and enables fast signal conduction.

Which hemisphere controls which side of the body?

Left hemisphere controls the right side; right hemisphere controls the left.

What connects the left and right hemispheres?

Corpus callosum (white matter) facilitates fast communication between hemispheres.

Forebrain vs Hindbrain overview

Forebrain includes the cerebrum and hypothalamus (thalamus mentioned in notes); Hindbrain includes the cerebellum, pons, and medulla oblongata; forebrain handles higher thinking, hindbrain governs basic automatic functions.

Cerebrum: overview and function

Largest part of the brain; responsible for higher thinking, personality, sensory perception, and vision; consists of two hemispheres and four lobes.

Frontal lobe: location and function

Front part of the brain; associated with higher-level thinking and personality.

Parietal lobe: location and function

Top of the brain; processes touch, temperature, and (in this teaching) taste.

Occipital lobe: location and function

Back of the brain; responsible for vision.

Temporal lobe: location and function

Located near the temples (by the ears); processes hearing and memory; interprets sensory information.

Hypothalamus: location and main functions

Below the thalamus; regulates homeostasis (temperature, fluid balance, hunger, thirst, sex drive, fight/flight) and connects to the pituitary for hormonal control.

Pituitary gland: function and nickname

Master gland; secretes hormones and controls other glands; connected to the hypothalamus and hangs from the brain.

Medulla oblongata: autonomic functions

Lower hindbrain structure; regulates autonomic processes like breathing, heart rate, and blood vessel diameter.

Pons: role in brain communication

Bridge between the spinal cord and brain; relay center; information passes through it.

Cerebellum: function

Little brain; coordinates balance, posture, and smooth muscle movements.

Left-right brain stereotype

Left hemisphere is often described as logical; right hemisphere as artistic (a simplified view).

What is the small space between the presynaptic and postsynaptic membranes called?

The synaptic cleft.

What are the chemicals released into the synaptic cleft called?

Neurotransmitters.

What triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft?

An arriving action potential at the synaptic knob that causes vesicles to fuse with the presynaptic membrane and release neurotransmitters via exocytosis.

What is the membrane of the neuron sending the signal called?

Presynaptic membrane.

What happens when a neurotransmitter binds to receptors on the postsynaptic membrane?

Ion channels (often sodium channels) open, allowing Na+ to enter and potentially trigger a postsynaptic action potential.

Which neurotransmitter is most commonly associated with muscle stimulation at the neuromuscular junction?

Acetylcholine (ACh).

Which enzyme breaks down acetylcholine in the synaptic cleft?

Acetylcholinesterase (cholinesterase).

What term describes the additive effect of multiple neurons converging on a single neuron to reach threshold?

Summation.

What is the difference between excitatory and inhibitory neurotransmitters?

Excitatory neurotransmitters increase the likelihood of an action potential; inhibitory neurotransmitters decrease it.

Name a neurotransmitter besides acetylcholine that plays a role in wakefulness and the fight-or-flight response.

Norepinephrine.

Why is brain transmission slower than reflex arcs?

Because transmission involves many synapses and diffusion is slow; reflex arcs involve only a few synapses (about 3–4).

What is the sequence of events at the synapse from the arrival of the action potential to postsynaptic depolarization?

Action potential arrives at the synaptic knob → synaptic vesicles release neurotransmitter into the synaptic cleft via exocytosis → neurotransmitter diffuses to the postsynaptic receptors → receptor binding opens sodium channels → Na+ influx → depolarization → possible initiation of a postsynaptic action potential.

What are presynaptic and postsynaptic membranes called?

Presynaptic membrane (sending side) and postsynaptic membrane (receiving side).

What happens to neurotransmitters after their action is finished to reset the synapse?

They are broken down or reabsorbed; for acetylcholine, acetylcholinesterase breaks it down.

Which toxin inhibits cholinesterase, leading to excessive acetylcholine and overstimulation?

Nerve gas (inhibits cholinesterase).

What is the drug discussed in the notes that inhibits cholinesterase to increase acetylcholine levels, and what does it do?

A cholinesterase inhibitor (referred to as donopazelle/donoprazole in the notes) that blocks cholinesterase and prevents breakdown of acetylcholine.

What is an example of a toxin that blocks sodium channels and causes paralysis?

Puffer fish toxin, which blocks sodium channels and prevents action potentials.

What are the three key items you need to know from the learning outcomes, as mentioned in the notes?

Acetylcholine, cholinesterase (the enzyme), and norepinephrine.

How do action potentials move along an axon?

They propagate like dominoes from the dendrite end toward the axon terminal, sequentially depolarizing adjacent sections.

Why does an action potential typically travel in one direction along the axon?

Because of the refractory period: recently depolarized areas are temporarily unexcitable until they reset, preventing backward propagation.

What speeds up the transmission of an action potential along an axon?

Myelination, which enables saltatory conduction where the impulse jumps between nodes of Ranvier.

What is saltatory conduction?

The rapid jumping of the action potential from one node of Ranvier to the next in a myelinated axon, speeding transmission.

What is the role of the myelin sheath?

Acts as an insulator that speeds conduction; gaps (nodes of Ranvier) contain many ion channels for action potential regeneration.

What are the nodes of Ranvier?

Gaps in the myelin sheath rich with ion channels where action potentials are regenerated.

What is multiple sclerosis (MS)?

An autoimmune disease where the immune system attacks myelin, destroying it and slowing nerve conduction.

How does MS affect nerve transmission?

Destruction of myelin slows conduction and can impair movement and sensation.

What is the all-or-none principle in neurons?

An action potential is either fully produced if threshold is reached or not produced at all; there are no partial action potentials.

What is a neuron’s threshold?

The minimum stimulus intensity required to trigger a full action potential (in the example, about 2 millivolts).

What happens during depolarization?

The inside of the neuron becomes more positive due to Na+ influx.

What happens during repolarization?

The membrane potential returns toward the resting negative value, largely due to K+ efflux.

What is polarization/resting potential?

The negative internal charge of a neuron when it is not firing; the resting potential is the state before depolarization.

What is the role of the Na+/K+ pump during the refractory period?

Helps reset ion concentrations to restore resting potential, enabling the neuron to be ready for another impulse.

Describe the frog nerve-muscle experiment and its relevance to threshold.

Stimulating a frog nerve connected to a muscle shows that 1 mV yields no contraction (below threshold), while 2 mV triggers an action potential and a measurable force (~3 newtons), illustrating the threshold and all-or-none response.

How does myelin affect the number of action potentials needed along an axon?

Myelin reduces the number of regenerations needed by allowing the impulse to skip insulated regions, speeding transmission.

What is another common term for the electrochemical impulse transmitted by neurons?

Action potential.

How can the electrochemical impulse be described, in terms of sequence along the axon?

As a series of action potentials that trigger neighboring segments, propagating like dominoes.

Which organism and structure were used to discover the action potential experimentally?

Giant squid axon; researchers used an oscilloscope and electrodes to measure voltage across the membrane.

What does the voltage trace look like during an action potential?

The inside becomes negative at rest, then becomes positive during depolarization, and returns to negative.

In neurons, which ions are primarily responsible for the action potential discussed in the notes?

Sodium (Na+) and potassium (K+).

What are voltage-gated ion channels?

Ion channels in the cell membrane that open or close in response to changes in membrane voltage.

At roughly what membrane potential do Na+ voltage-gated channels open (threshold)?

Around -50 mV (threshold), though it varies by neuron.

At what membrane potential do Na+ voltage-gated channels close?

Approximately +40 mV.

What happens during depolarization?

Sodium ions rush into the axon, making the inside more positive.

What happens during repolarization?

Potassium ions exit the cell, returning the inside toward negative; Na+ channels close and K+ channels remain open for a short time.

What is hyperpolarization?

A brief return below the resting potential after repolarization.

What is resting membrane potential?

The polarized, ready state of the neuron; typically around -70 mV, but can vary (e.g., -90 mV in some cases).

What does the sodium-potassium pump do?

Pumps 3 Na+ out and 2 K+ in using ATP, helping maintain the resting membrane potential.

What is diffusion in this context?

Movement of ions down their concentration gradient through channels.

What is threshold in the context of action potentials?

The membrane potential that triggers opening of Na+ voltage-gated channels, initiating depolarization.

What is the 'salt banana' analogy used for resting potential?

Outside is high in Na+ and outside is positive; inside has higher K+ and is negative, illustrating resting potential.

What is the refractory period?

A period after an action potential during which the neuron is less excitable or cannot fire again until gradients are re-established.

How does the sodium-potassium pump contribute to the resting potential after the action potential?

By restoring the ion concentrations (3 Na+ out, 2 K+ in), it helps reestablish the negative interior.

Which ion movement dominates during depolarization and repolarization?

Depolarization: Na+ influx; Repolarization: K+ efflux.

Why is myelin mentioned in the notes?

To indicate that myelin speeds up the conduction of the action potential; to be covered in a future lesson.

What are the three main types of neurons?

Sensory (afferent) neuron, interneuron, and motor (efferent) neuron; interneurons are located in the CNS.

Where are interneurons located?

In the central nervous system (brain and spinal cord) only.

What does a sensory neuron do?

It carries sensory information into the CNS (toward the brain/spinal cord).

What does a motor neuron do?

It carries information out of the CNS to an effector (muscle, gland, or organ) to trigger a response.