The nervous system

What are the main divisions of the nervous system?

CNS (brain, spinal cord), PNS (sensory, motor: somatic, autonomic).

Name the lobes of the cerebral cortex and their separating sulci

Frontal, Parietal (central sulcus), Temporal (lateral sulcus), Occipital (parieto-occipital sulcus).

What are the three layers of the meninges?

Dura mater (outer), Arachnoid mater (middle), Pia mater (inner).

How is the spinal cord segmented?

31 segments: Cervical (8), Thoracic (12), Lumbar (5), Sacral (5), Coccygeal (1).

Classify neurons by connections.

Sensory (afferent): To CNS. Interneurons: Within CNS. Motor (efferent): From CNS to muscles/glands.

What is the resting membrane potential, and why is it closer to K⁺’s equilibrium potential?

RMP is ~ -70 mV (inside negative). It’s closer to K⁺’s equilibrium potential (-90 mV) because the membrane is 25-30 times more permeable to K⁺ than Na⁺ at rest.

What triggers the opening of Na⁺ channels during action potential generation?

Stimuli like neurotransmitters, external chemicals (e.g., olfaction), or physical pressure (e.g., touch) trigger ligand-gated or mechanically gated Na⁺ channels to open.

What are the two types of summation in synaptic transmission?

Spatial summation (multiple synapses firing simultaneously) and temporal summation (one synapse firing repeatedly).

What are the steps of neurotransmitter release at a chemical synapse?

1. Action potential reaches axon terminal. 2. Voltage-gated Ca²⁺ channels open. 3. Ca²⁺ binds to sensor protein. 4. Ca²⁺-protein complex triggers vesicle fusion and exocytosis.

How is acetylcholine removed from the synaptic cleft?

Broken down into acetate and choline by acetylcholinesterase.

What are the main functions of the nervous system?

Sensory input (detects stimuli), integration (processes info in CNS), motor output (commands to effectors), homeostasis (regulates internal environment), and protection (reflexes to avoid harm).

What are the two main divisions of the nervous system, and their roles?

CNS (brain, spinal cord): integration and processing. PNS (cranial/spinal nerves): sensory input and motor output to the body.

What is the role of the cerebral cortex in the CNS?

Processes sensory info, plans movement, and handles higher functions: frontal (movement, speech), parietal (touch), occipital (vision), temporal (hearing, language).

How is the PNS functionally organized, and what are the roles of its components?

Cranial nerves (12 pairs): innervate head (sensory/motor). Spinal nerves (31 pairs): sensory (receptors) and motor (muscles) for body. Dermatomes: map sensory skin areas.

What is the difference between the somatic and autonomic divisions of the PNS?

Somatic: Voluntary movement (skeletal muscle, one neuron, ACh). Autonomic: Involuntary (smooth/cardiac muscle, glands, two-neuron chain, ACh/NE).

What is a reflex, and what are its main functions?

A rapid, involuntary response to a stimulus. Functions: protection (e.g., withdrawal), control (e.g., muscle length), homeostasis, and posture/balance.

What is the difference between monosynaptic and polysynaptic reflex arcs?

Monosynaptic: One synapse, no interneurons (e.g., knee jerk). Polysynaptic: Involves interneurons for coordination (e.g., withdrawal reflex).

How does the knee jerk reflex work as a control reflex?

Muscle spindle detects stretch → sensory neuron → spinal cord → motor neuron → quadriceps contraction (monosynaptic). Controls muscle length (closed loop).

How does the flexion withdrawal reflex work as a protective reflex?

Pain receptor → sensory neuron → interneurons → motor neurons → flexor contraction to withdraw limb (polysynaptic). Protects by avoiding harm (open loop).

Why are reflex circuits suited for control and protective functions?

Speed (monosynaptic = fast), subconscious (bypasses brain), stereotyped (predictable), and polysynaptic reflexes coordinate complex protective movements (e.g., withdrawal, crossed extensor).

What is the main function of the sympathetic nervous system?

"Fight or Flight" - prepares body for stress (↑ heart rate, bronchodilation, pupil dilation).

What is the main function of the parasympathetic nervous system?

"Rest and Digest" - promotes energy conservation (↓ heart rate, ↑ GI motility, pupil constriction).

What is the enteric nervous system and its role?

"Second brain" in GI tract; autonomously controls peristalsis and secretion.

What neurotransmitters are used in the sympathetic NS?

Preganglionic: Acetylcholine (ACh); Postganglionic: Norepinephrine (NE).

What neurotransmitters are used in the parasympathetic NS?

Preganglionic and Postganglionic: Acetylcholine (ACh).

What are the receptor types for the ANS?

Sympathetic: Adrenergic (α1, α2, β1, β2); Parasympathetic: Muscarinic (M1, M2, M3).

What is the role of the adrenal medulla in the ANS?

Modified sympathetic ganglion; secretes adrenaline (75-80%) and norepinephrine into blood.

What is the baroreflex?

Reflex that detects ↑ arterial pressure, ↑ parasympathetic and ↓ sympathetic activity to ↓ heart rate.

Name a muscarinic antagonist and its use.

Atropine; dilates pupils, prevents parasympathetic reflexes in surgery.

Name a beta-adrenergic agonist and its use.

Salbutamol; promotes bronchodilation for asthma relief.

How does the somatic NS differ from the ANS?

Somatic: Voluntary, single neuron, ACh (nicotinic); ANS: Involuntary, two neurons, ACh/NE (muscarinic/adrenergic).

Name three diseases linked to ANS dysregulation.

Hypertension, depression, Alzheimer’s.