Neuroscience and Neurotransmission: Nervous System, Brain Anatomy, and Synaptic Function

Central Nervous System (CNS)

Includes brain + spinal cord. Responsible for processing, integrating, and issuing commands.

Peripheral Nervous System (PNS)

Connects the CNS to the rest of the body.

Cranial nerves

12 pairs that originate directly from the brain/brainstem.

Efferent (motor)

Carry commands from CNS to muscles and glands.

Afferent (sensory)

Carry input from sensory receptors to CNS.

Spinal nerves

31 pairs that branch off spinal cord; each has sensory (dorsal root) and motor (ventral root) components.

Autonomic Nervous System (ANS)

Governs involuntary physiological processes: HR, BP, respiration, digestion, arousal.

Sympathetic NS

Prepares body for action (↑ HR, ↑ blood flow to muscles, dilated pupils, ↓ digestion). Uses norepinephrine as the primary neurotransmitter.

Parasympathetic NS

Promotes homeostasis (↓ HR, ↑ digestion, energy storage). Uses acetylcholine at target organs.

Meninges

Three layers surrounding brain/spinal cord: Dura mater, Arachnoid mater, Pia mater.

Dura mater

Tough, outer protective layer.

Arachnoid mater

Middle layer with CSF-filled subarachnoid space.

Pia mater

Thin, delicate layer adhering directly to brain/spinal cord.

Ventricles & CSF

Four interconnected ventricles filled with cerebrospinal fluid (CSF). CSF cushions the brain, removes waste, and regulates intracranial pressure.

Myelencephalon

Develops into the medulla, responsible for autonomic functions - breathing, heart rate, blood pressure.

Metencephalon

Includes pons (sleep, arousal, relay) + cerebellum (motor coordination, balance, procedural learning).

Mesencephalon

Includes tectum (superior colliculi for visual reflexes, inferior colliculi for auditory reflexes) and tegmentum (reticular formation, periaqueductal gray, substantia nigra, ventral tegmental area, red nucleus).

Thalamus

Relay station for nearly all sensory input to cortex.

Hypothalamus

Maintains homeostasis (temperature, hunger, thirst, circadian rhythms, hormone release). Links nervous system to endocrine system via the pituitary gland.

Limbic system

Involved in emotional regulation + memory. Includes amygdala, hippocampus, cingulate cortex, fornix, septum, mammillary bodies.

Basal ganglia

Involved in motor control, habit formation, procedural learning.

Cerebral cortex

Responsible for higher cognition, language, perception, voluntary movement.

Frontal lobe

Includes primary motor cortex (initiates voluntary movement) and association cortex (executive functions).

Parietal lobe

Includes primary somatosensory cortex (processes touch, pain, temperature, proprioception) and association cortex (body/spatial awareness).

Temporal lobe

Includes primary auditory cortex (first cortical processing site for sound) and association cortex (language comprehension, auditory/visual object recognition).

Occipital lobe

Includes primary visual cortex (detects patterns, static/moving objects).

Association cortex

Interprets complex visual info, spatial relations.

Neuron

Specialized cell for communication via electrical and chemical signals.

Glial cells

Support neuronal function.

Astrocytes

Maintain extracellular environment, provide nutrients, form blood-brain barrier.

Oligodendrocytes

Form myelin sheaths in the CNS.

Schwann cells

Form myelin sheaths in the PNS.

Satellite cells

Support neurons in PNS ganglia.

Resting potential

≈ -70 mV, maintained by Na⁺/K⁺ pump and selective membrane permeability.

Action Potential

Triggered when depolarization reaches threshold (~ -55 mV).

Depolarization

Voltage-gated Na⁺ channels open → Na⁺ influx.

Repolarization

K⁺ channels open → K⁺ efflux.

Hyperpolarization

Overshoot below resting potential.

Self-propagation

AP regenerates along axon; strength does not decrease with distance.

Chemical synapse

AP triggers vesicle fusion → NT release into synaptic cleft.

Electrical synapse

Direct ion flow between cells; extremely fast but less flexible.

EPSPs

NT binding depolarizes postsynaptic neuron (more likely to fire).

IPSPs

NT binding hyperpolarizes (less likely to fire).

Temporal summation

Multiple signals over time from one input combine.

Spatial summation

Inputs from multiple sources combine.

Glutamate

Most common excitatory NT in CNS; involved in synaptic plasticity and learning.

GABA

Most common inhibitory NT; involved in anxiety regulation, sedation, seizure prevention.

Acetylcholine (ACh)

Primary NT at neuromuscular junction; controls skeletal muscle contraction.

Monoamines

Neurotransmitters derived from amino acids, including dopamine and serotonin.

Monoamine Oxidase (MAO)

Enzyme that breaks down neurotransmitters like norepinephrine, epinephrine, dopamine, and serotonin.

Agonists

Substances that enhance NT activity.

Antagonists

Substances that block NT activity.