Autonomic nervous system

Input of afferent division of autonomic nervous system

Somatic stimuli from skin + muscles

Function of afferent division

Generate nerve impulses from stimuli to be transmitted to the central nervous system

Function of efferent division

Transmit nerve impulses from CNS to the effector organs

Function of somatic afferent division of ANS

→ regulate voluntary movement by skeletal muscles 

Function of somatic nervous system

→ controls voluntary movement by skeletal muscles 

Function of autonomic nervous system

→ controls involuntary functions: sympathetic + parasympathetic 

→ affects organs, glands, smooth muscles 

Functions of enteric nervous system

controls involuntary digestion

Function of sympathetic + parasympathetic nervous systems

Sympathetic + parasympathetic nervous systems: innervate same organs but have opposite effects 

Function: maintaining homeostasis 

Action of sympathetic nervous system

1. Increases heart rate 

2. Dilates bronchi 

3. Shuts down digestion + excretion 

4. Mobilise glucose for use by muscles 

5. Releases adrenaline 

6. Activation of sweat glands

Action of parasympathetic nervous system

1. Heart rate slows 

2. Bronchi constrict 

3. Digestion + excretion promoted 

4. Glucose taken up into cells 

5. Increased secretion by salivary + digestive glands

Features of pre + postganglionic neurons of sympathetic NS

Short preganglionic fibre + long postganglionic fibre

Features of pre + postganglionic neurons of parasympathetic NS

Long preganglionic + short postganglionic fibres

Location of sympathetic NS origin + ganglion

Origin: T1 - L2/3

Ganglion: paravertebral ganglionic chain

Location of parasympathetic NS origin + ganglion

Origin: C3, 7,9,10/ S2-4

Ganglion: in/ near target organs

Types of structures secreting acetylcholine

Cholinergic neurons  Preganglionic neurons  Parasympathetic postganglionic nerves  Sympathetic postganglionic neurons for sweat gland

Types of structures secreting noradrenaline

1. Adrenergic neurons 

2. Sympathetic posganglionic nerves

Types of structures secreting adrenaline

Adrenal medulla

Determinants of speed of signalling

1. Myelin sheath → insulating axon from ECF 

2. Type of cells: schwann cells in PNS/ oligodendrocytes in CNS 

Types of axon fibres + features

Axon type	Diameter	Degree of myelination	Conduction velocity
Group A	Large	Heavily	Fastest
Group B	Intermediate	Lightly	Middle
Group C	Small	N	Slowest

What types of axon fibres do somatic + autonomic nervous system have

Division of nervous system	No of neurons	Type of axons	Conduction velocity
Somatic	1	A type	Fastest
Autonomic	2 ( preganglionic + postganglionic neurons )	B + C type	Slower

Function of adrenal medulla

• acts like a modified autonomic ganglion 

Function: secretes hormones ( adrenaline + noradrenaline ) into blood by stimulation of preganglionic fibre

What is dual innervation + autonomic tone + function

Dual innervation: when organs are innervated by both sympathetic + parasympathetic nervous system

Autonomic tone: when sympathetic + parasympathetic NS are both tonically active

Function: rapid + precise regulation of tissue function

Examples of dually + singly innervated organs

Examples of dually innervated organs: 

Heart 

Examples of singly innervated organs 

Liver: X parasympathetic innervation; only sympathetic innervation → glycogenolysis 

Sweat glands

Adipose cells: X parasympathetic innervation; only sympathetic innervation → lipolysis 

Why does the autonomic nervous system have different effects on skeletal muscles vs smooth muscles + glands

Skeletal muscles have well defined neuroeffector junctions while smooth muscles + glands have autonomic varicosities 

Differences bwt neuroeffector junction + autonomic varicosities

	Neuroeffector junction	Autonomic varicosities
Target tissues	Skeletal muscle fibres	Smooth muscle, glands, adipose tissue
Structures	One specialised synapse	Multiple bead like varicosities
Neurotransmitters	Acetylcholine	Acetylcholine + noradrenaline
Response	Fast, precise, short lasting	Slower, diffuse, long lasting
Function	Highly coordinated + precise control	Broad, graded influence over a whole organ/ region