Exam 2: Neuroscience and Sensory Systems: Neurons, Brain, and Cranial Nerves

Cell Body

The part of the neuron that contains the nucleus and organelles.

Dendrites

Branch-like structures that receive signals from other neurons.

Schwann (PNS)

Cells that form the myelin sheath around axons in the peripheral nervous system.

Axon terminals

The endpoints of an axon where neurotransmitters are released.

Axon

The long, slender projection of a neuron that conducts electrical impulses away from the cell body.

Nucleus

The organelle in the cell body that contains genetic material.

Frontal

The lobe of the brain associated with reasoning, planning, and problem-solving.

Temporal

The lobe of the brain associated with processing auditory information and memory.

Occipital

The lobe of the brain primarily responsible for visual processing.

Parietal

The lobe of the brain that processes sensory information such as touch and temperature.

Resting Membrane Potential

-Neuron sits at about -70 mV

-Maintained by the Na+/K+ pump (3 Na+ out, 2 K+ in) and K+ leak channels

Depolarization

- A stimulus causes membrane potential to become less negative

- If it reaches threshold (~ -55 mV), voltage-gated Na+ channels open

- Na+ rushes into the cell - rapid depolarization

Rising Phase

- Membrane potential shoots up toward +30 mV as Na+ floods in

- Positive feedback: more depolarization - more Na+ channels open

Repolarization

- At peak (~+30 mV), Na+ channels inactivate

- Voltage-gated K+ channels open, K+ flows out of the cell

- Membrane potential moves back toward negative

Hyperpolarization (Undershoot)

- K+ channels close slowly - extra K+ leaves

- Membrane dips below resting potential (~ -80 mV)

Return to Resting Potential

- K+ channels fully close

- Na+/K+ pump restores -70 mV resting state

Absolute refractory period

The period during which no new action potential can be initiated due to inactivation of Na⁺ channels.

Relative refractory period

The period during which a stronger stimulus can trigger an action potential because the membrane is hyperpolarized.

Afferent

Refers to sensory input

Afferent fibers

Carry information from sensory receptors throughout the body toward the central nervous system

Efferent

Refers to motor output

Efferent fibers

Carry instructions from the central nervous system to effectors such as muscles and glands

Somatic

- Related to the body wall (skin, skeletal muscles, joints)

- Deals with voluntary control and conscious perception

Visceral

- Relates to the internal organs (smooth muscle, cardiac muscle, glands)

- Deals with involuntary control and unconscious regulation

Primary Function of the Nervous System

Performs 3 main tasks: Sensory Input, Integration, Motor Output

Sensory Input

Sensory (afferent) receptors detect and monitor changes inside and outside the body

Integration

The central nervous system processes and interprets sensory input, making decisions about what should happen next

Motor Output

The nervous system sends efferent signals to muscles, glands, or organs to produce a response

Central nervous system (CNS)

Brain and spinal cord; serves as the control center for processing and integration

Peripheral Nervous System (PNS)

Cranial nerves and spinal nerves that connect the central nervous system to the rest of the body

Sensory (Afferent) Division

Carries instructions from sensory receptors to the central nervous system

Motor (Efferent) Division

Carries instructions from the central nervous system to effectors

Somatic nervous system (SNS)

Voluntary control of skeletal muscles

Autonomic nervous system (ANS)

Involuntary control of smooth muscle, cardiac muscle, and glands

Sympathetic Division

"Fight or flight" responses

Parasympathetic Division

"Rest and digest" responses

Sensory (afferent)

Transmits info from receptors to central nervous system

Motor (efferent) neurons

Transmits commands from central nervous system to effectors (muscles, glands)

Somatic motor

voluntary control of skeletal muscles

Autonomic motor

- Involuntary control (smooth muscle, cardiac muscle, glands)

- Sympathetic vs parasympathetic

Somatic sensory

from skin, skeletal muscles, joints

Visceral sensory

From internal organs (Ex: stretch, pain, chemical signals)

Nucleus

Collection of cell bodies in the central nervous system

Ganglion

Collection of cell bodies in the peripheral nervous system

Tract

Bundle of axons in the central nervous system

Nerve

Bundle of axons in the peripheral nervous system

Cell body (soma)

Contains nucleus, metabolic center

Dendrite function

Receive signals

Axon

Transmits impulses away

Axon hillock

Trigger zone for action potential

Axon terminals

Release neurotransmitters

Multipolar

Many dendrites, one axon; found in central nervous system and motor neurons

Bipolar neuron

One dendrite, one axon; found in sensory organs (eye, ear, olfactory)

(Pseudo)Unipolar

Single process splits into peripheral and central branches; most sensory neurons

Sensory neurons

Afferent, carry input into central nervous system

Interneurons

Association neurons in central nervous system, processes and integrate

Motor neurons

Efferent, carry commands to effectors

Six neuroglia

Astrocytes, microglia, ependymal, oligodendrocytes, satellite cells, schwann cells

Astrocytes (CNS)

Support, regulate chemical environment in the central nervous system

Microglia (CNS)

Immune defense, transform into macrophages

Ependymal cells (CNS)

Line ventricles, circulate cerebrospinal fluid

Oligodendrocytes (CNS)

Myelinate multiple axons in central nervous system

Satellite cells (PNS)

Support peripheral nervous system neuron cell bodies

Schwann cells (PNS)

Myelinate axons (one segment each) in peripheral nervous system

Myelination function

Wrapping axons with lipid-rich sheath for insulation; inccreases signal conduction

Myelination function

increases speed of impulse conduction

CNS myelination

oligodendrocytes wrap multiple axons

PNS myelination

schwann cells wrap only one axon segment

Large axon diameter

faster conduction (less resistance)

Myelination

faster conduction (saltatory vs continuous)

Major Ion Channels

Leak channels, ligand-gated, mechanically gated, voltage-gated

Leak channels

Na+ in, K+ out (constant)

Ligand-gated channels

open when neurotransmitter binds

Mechanically gated channels

open with pressure/tension

Voltage-gated channels

open/close at threshold voltages (Na+ fast, K+ slower)

Steps of an Action Potential

1. Local depolarization at axon hillock

2. Threshold reached (about -50 mV)

3. Na+ influx - rapid depolarization

4. Peak (+35-50 mV): Na+ channels close, K+ channels open

5. K+ efflux - repolarization

6. Excess K+ outflow - hyperpolarization

7. Return to resting potential (-70mV)

Depolarization

membrane potential becomes less negative

Repolarization

Membrane potential returns toward resting

Hyperpolarization

more negative than resting

Threshold

Critical voltage (about -50 mV) to trigger AP

Local (graded) potentials

short distance, graded, decremental, reversible, excitatory or inhibitory

Action potentials

long distance, all-or-none, non-decremental, irreversible

salatory conduction

the process by which action potentials are conducted in myelinated neurons

Role of myelin

action potentials jump node to node (nodes of ranvier)

Effect of salatory conduction

much faster than continuous conduction in unmyelinated axons

Neurotransmitters

Excitatory, inhibitory, biogenetic amines, acetylcholine, neuropeptides

excitatory neurotransmitters

- Ex: glutamate

- central nervous system

- stimulate depolarization

Inhibitory neurotransmitters description

- Ex: GABA, glycine

- central nervous system

- hyperpolarization

Biogenic amines

- Ex: dopamine, serotonin, norepinephrine

- mood, arousal, motor control

Acetylcholine neurotransmitters

- neuromuscular junction, parasympathetic synapses

Neuropeptides

- Ex: endorphins, substance P

- pain modulation, reward

Cerebrum

- Largest brain region

- two hemispheres

- responsible for higher functions

Diencephalon

- central core

- contains thalamus, hypothalamus, epithalamus

Brain stem

midbrain, pons, medulla

Cerebellum

coordination and timing of movement

white matter

myelinated neurons

grey matter

non-myelinated neurons

Major lobes

frontal, parietal, temporal, insula

Major fissures/sulci

longitudinal fissure, lateral sulcus, central sulcus, transverse fissure

Motor areas

primary motor cortex (precentral gyrus), premotor cortex, broca's area, frontal eye field