Unit 6

Receiving Sensory Input

Detects internal and external stimuli through sensory receptors.

Integrating Information

Processes, analyzes, and stores sensory input to determine the appropriate response.

Controlling Muscles and Glands

Sends signals to effectors to initiate movement or secretion.

Maintaining Homeostasis

Regulates vital body functions (like temperature and blood pressure) to keep the internal environment stable.

Establishing and Maintaining Mental Activity

Supports consciousness, memory, thinking, emotions, and learning.

Central Nervous System (CNS)

Composed of the Brain and Spinal Cord. It acts as the main processing and control center.

Peripheral Nervous System (PNS)

All nervous tissue outside the CNS. It connects the CNS to the rest of the body.

Somatic Nervous System

Involved in conscious (voluntary) perception and control.

Autonomic Nervous System (ANS)

Controls involuntary functions (e.g., heart rate, digestion).

Motor Division

Transmits action potentials from the CNS to effector organs.

Sympathetic Division

Prepares the body for physical activity ('Fight or Flight').

Parasympathetic Division

Regulates resting functions like digestion ('Rest and Digest').

Enteric Nervous System (ENS)

A semi-independent network of sensory and motor neurons located entirely within the Gastrointestinal Tract (GIT) to control digestion.

Neurons

The primary structural and functional units. They receive stimuli, transmit signals, and send action potentials to other neurons or effector organs.

Cell Body (Soma)

The core control center of the neuron.

Dendrites

Short, branching extensions that receive information and send it toward the cell body.

Axon

A single, long extension that sends information away from the cell body.

Epineurium

The outermost layer that covers the entire nerve.

Perineurium

The middle layer that surrounds bundles (fascicles) of axons.

Endoneurium

The innermost layer that surrounds each individual axon.

Multipolar Neuron

Has many dendrites and one axon (most common type).

Bipolar Neuron

Has a single dendrite and a single axon (found in special senses like the eye).

Pseudo-unipolar Neuron

Has a single process extending from the cell body that soon splits into two branches.

Anaxonic Neuron

Has no distinguishable axon; it appears to have only dendrites (or no apparent axon).

Astrocytes

Star-shaped cells that stimulate/inhibit nearby neuronal signals and form the blood-brain barrier (BBB) to protect the brain from harmful substances.

Ependymal cells

Line the fluid-filled cavities of the brain and spinal cord; produce and circulate cerebrospinal fluid.

Microglia

Act as the immune defense of the central nervous system; remove cellular debris, waste, and pathogens (phagocytosis).

Oligodendrocytes

Form the myelin sheath around axons in the central nervous system (CNS).

Satellite cells

Support peripheral neurons and provide nutrients to them in the peripheral nervous system (PNS).

Gray Matter

Made of cell bodies, dendrites, and unmyelinated axons.

White Matter

Made of bundles of parallel axons wrapped in a myelin sheath.

Resting Membrane Potential

The charge difference across the cell membrane when the cell is at rest.

Polarized Cell

A cell that exhibits an uneven distribution of charge across its membrane.

Leak Channels

These channels are always open.

Function of Leak Channels

Ions move continuously through them down their concentration gradient.

Role of Leak Channels

They are primarily responsible for maintaining the baseline resting membrane potential.

Gated Ion Channels

These channels open and close in response to specific stimuli.

Voltage-Gated Channels

Open or close in response to changes in the membrane potential (charge).

Ligand-Gated (Chemically-Gated) Channels

Open or close when a specific chemical (like a neurotransmitter) binds to them.

Mechanically-Gated Channels

Open or close in response to physical distortion of the membrane (like touch or pressure).

Sodium-Potassium Pump

Actively pumps 3 Na⁺ out for every 2 K⁺ in to maintain the gradient.

Action Potential Propagation

The electrical impulse travels like a wave down the length of the axon.

Depolarization

A stimulus causes voltage-gated Na⁺ channels to open, causing the inner membrane potential to spike from negative toward positive values.

Repolarization

Voltage-gated Na⁺ channels close and K⁺ channels open, restoring the negative internal charge.

Hyperpolarization

The K⁺ channels stay open slightly too long, causing the membrane potential to briefly dip below -70 mV.

Synapse

The meeting point between the axon of one neuron and another neuron or an effector organ (like a muscle).

Presynaptic Terminal

Chemical messengers called neurotransmitters are stored in tiny sacs (synaptic vesicles) at the end of the axon.

Calcium Entry

An electrical signal (action potential) reaches the end of the axon, opening calcium channels.

Signal Release

The calcium helps release the neurotransmitters into the space between the cells.

Cholinergic Neurotransmitter

Acetylcholine (ACh) is a common type of neurotransmitter.

Norepinephrine (NE)

Typically has an excitatory effect at the synapse in the CNS and ANS.

Dopamine

Can be excitatory or inhibitory depending on the receptor type.

Gamma-Aminobutyric Acid (GABA)

A major neurotransmitter found in the CNS that produces an inhibitory effect at the synapse.

Converging Pathway

Two or more presynaptic neurons synapse with the same single postsynaptic neuron.

Diverging Pathway

The axon of one neuron divides and synapses with more than one postsynaptic neuron.

Spatial Summation

Multiple local potentials occur at different locations on the postsynaptic neuron at the same time to reach threshold.

Cerebrum

The largest part of the brain, subdivided into left and right hemispheres.

Gyri

Folds or ridges on the surface of the cerebrum that increase the surface area of the cortex.

Sulci

Shallow grooves between the gyri that further divide the brain into distinct lobes.

Action Potential

Depolarization & repolarization

Repolarization

Outward flow of K causes cell membrane back to resting membrane potential.

Hyperpolarization

More (-) charges than resting membrane potential.

All-or-none action potential

An action potential that is started.

Depolarization Phase

Resting membrane potential voltage of -70mV rises to +20mV.

Repolarization Phase

Resting membrane potential voltage returns to -70mV.

Synapse

Junction where axon of one neuron meets with another neuron or with cells of effector organs.

Presynaptic terminal

Ends of the axon.

Postsynaptic membrane

Membrane of dendrite or effector cell.

Synaptic cleft

Space in-between presynaptic and postsynaptic membranes.

Neurotransmitters

Chemical substances stored in synaptic vesicles at presynaptic terminal.

Calcium influx

Ca moves into cell, releasing neurotransmitters.

Cholinergic neurotransmitter

Acetylcholine (ACh) - CNS synapses as excitatory and ANS synapses as inhibitory.

Norepinephrine (NE)

Some CNS & ANS synapses; excitatory effect.

Dopamine

CNS/ANS; excitatory/inhibitory.

Serotonin

CNS synapse with inhibitory effect.

Gamma-aminobutyric acid (GABA) and Glycine

Amino Acid CNS synapses with inhibitory effect.

Endorphin

Peptide that blocks pain pathways.

Central Nervous System

Consists of brain and spinal cord.

Cerebrum

Largest part of the brain, subdivided into R & L hemispheres.

Frontal lobe

Controls voluntary motor function, motivation, aggression, mood & olfactory reception.

Parietal lobe

Main center for sensory info like touch, pain, temperature & balance.

Occipital lobe

Receives and perceives visual input.

Temporal lobe

For olfactory & auditory sensations, role in memory.

Thalamus

Largest part of diencephalon; sensory input passing from spinal cord & brainstem go to thalamus neuron.

Hypothalamus

Controls body temperature, hunger & thirst, affects emotional responses.

Cerebellum

Involved in maintaining balance, muscle tone & coordinating fine motor movement.

Brainstem

Connects the spinal cord to the brain.

Medulla oblongata

Regulates heart rate, blood vessel diameter, breathing, swallowing, vomiting, coughing, sneezing, balance and coordination.

Pons

Functional bridge between cerebrum and cerebellum.

Reticular formation

Regulates cyclical motor functions: respiration, walking, chewing.

Basal nuclei

Group of functionally related nuclei involved in planning, organizing, coordinating motor movements and posture.

Spinothalamic tract

Transmit sensations of pain & temperature to thalamus, then to cerebral cortex.

Dorsal column

Transmit sensations of touch, pressure, proprioception and vibration.

Primary sensory areas

Ascending tracts go to specific region of cerebral cortex & perceived sensations like visual, auditory cortex, taste at insula.

Primary somatosensory cortex

General sensory area at parietal lobe, posterior to central sulcus.

Somatic motor system

Responsible for keeping body's posture and balance, movement of trunk, head, limbs, tongue, eyes.

Involuntary movements

Reflexes mediated by spinal cord & brainstem, occur without conscious thought.

Voluntary movement

Consciously activated to move.

Direct pathway

Sends motor responses from upper motor neuron in cerebral cortex to lower motor neurons in spinal cord or brainstem.

Lateral corticospinal tract

Skilled movements of hand.