NEURAL CONTROL AND COORDINATION · Comparison Tables

1. CNS vs PNS; Afferent vs Efferent Fibres

Feature	CNS	PNS
Components	Brain and spinal cord	All nerves associated with CNS
Primary role	Information processing and control	Links CNS with body tissues and organs

Fibre	Direction of impulse	Role
Afferent	Tissues / organs -> CNS	Brings sensory input to CNS
Efferent	CNS -> peripheral tissues / organs	Carries regulatory output

2. Somatic vs Autonomic vs Visceral Nervous System

Division	Target / arrangement	Function
Somatic neural system	Skeletal muscles	Relays CNS impulses to skeletal muscles
Autonomic neural system	Involuntary organs and smooth muscles; includes sympathetic and parasympathetic divisions	Transmits CNS impulses to involuntary effectors
Visceral nervous system	Complex PNS network of nerves, fibres, ganglia and plexuses between CNS and viscera	Conducts impulses in both directions between CNS and viscera

3. Dendrites vs Axon; Neuron Types

Feature	Dendrites	Axon
Structure	Short and repeatedly branched projections with Nissl’s granules	Usually single long fibre; distal end branches into synaptic knobs
Impulse direction	Towards cell body	Away from cell body to synapse or neuromuscular junction
Terminal function	Receives / conducts input to soma	Synaptic vesicles in knob contain neurotransmitters

Neuron type	Processes	Example
Multipolar	One axon, two or more dendrites	Cerebral cortex
Bipolar	One axon, one dendrite	Retina
Unipolar	Cell body with one axon only	Usually embryonic stage

4. Myelinated vs Non-myelinated Fibres

Feature	Myelinated nerve fibre	Non-myelinated nerve fibre
Schwann-cell relation	Schwann cells form myelin sheath around axon	Schwann cell encloses axon but does not form myelin sheath
Nodes of Ranvier	Present as gaps between adjacent myelin sheaths	Not present
Occurrence	Spinal and cranial nerves	Common in autonomic and somatic neural systems

5. Resting Potential vs Action Potential

Feature	Resting potential / polarised state	Action potential / depolarised state
Membrane permeability	More permeable to K⁺, nearly impermeable to Na⁺ and negative proteins	Stimulus briefly makes membrane freely permeable to Na⁺
Ion distribution	Inside: high K⁺, negative proteins, low Na⁺; outside: high Na⁺, low K⁺	Rapid Na⁺ influx at stimulus site
Charge pattern	Outer surface positive, inner surface negative	Polarity reverses: outer becomes negative, inner positive
Maintenance / recovery	Na⁺-K⁺ pump sends 3 Na⁺ out for 2 K⁺ in	Subsequent K⁺ permeability rise permits K⁺ efflux and repolarisation

6. Electrical vs Chemical Synapse

Feature	Electrical synapse	Chemical synapse
Membrane relation	Pre- and post-synaptic membranes are very close	Fluid-filled synaptic cleft separates membranes
Transmission	Electrical current passes directly between neurons	Action potential triggers vesicle fusion and neurotransmitter release; transmitter binds specific post-synaptic receptors
Speed / occurrence	Faster; rare in human neural system	Slower than electrical synapse; common mechanism
Result	Like conduction along one axon	Ion channels open and new excitatory or inhibitory potential is produced

7. Forebrain Structures

Structure	Key structure	Major function
Cerebrum	Largest part; two hemispheres linked by corpus callosum. Cortex is grey matter; inner myelinated tracts are white matter.	Motor, sensory and association functions; memory and communication.
Thalamus	Wrapped by cerebrum	Major coordinating centre for sensory and motor signalling.
Hypothalamus	At base of thalamus; contains neurosecretory cells	Temperature, eating, drinking and hypothalamic hormones.
Limbic system	Inner cerebral hemispheres plus deep structures such as amygdala and hippocampus	Sexual behaviour, emotion, motivation, excitement, pleasure, rage and fear.

8. Midbrain vs Hindbrain Components

Region	Location / structure	Function
Midbrain	Between thalamus/hypothalamus and pons; cerebral aqueduct passes through it; dorsal corpora quadrigemina	Integrates visual, tactile and auditory inputs
Pons	Part of hindbrain and brain stem	Fibre tracts interconnect brain regions
Cerebellum	Highly convoluted surface	Integrates information for balance and coordination
Medulla oblongata	Connects to spinal cord; part of brain stem	Controls respiration, cardiovascular reflexes and gastric secretions

Brain stem Midbrain, pons and medulla oblongata together connect brain and spinal cord. The brain is covered by dura mater, arachnoid and pia mater beneath the skull.