Somatic vs autonomic vs visceral nervous system, and where do sensory neurons fit? I need a clean tree
Diya Menon11th Sample
12 Sept 2026 · 1 min read
Ahh I thought neural control would be my favourite chapter but the first page already got me 😭
The part I understood: Hydra has a simple nerve net, insects have a brain and some ganglia, vertebrates have a much more developed system. In humans the neural system is divided into the CNS (brain and spinal cord) and the PNS (all the nerves associated with the CNS).
The PNS is where my brain melts. NCERT says it has afferent fibres and efferent fibres. Afferent carry impulses from tissues/organs to the CNS and efferent carry regulatory impulses from the CNS to the peripheral tissues. Then the efferent division is further divided into somatic and autonomic. And somewhere there's a "visceral nervous system" which sounds like a third system?
My doubts:
- Where do sensory neurons go in the tree? Under afferent only?
- Is the autonomic system a part of the PNS or a separate thing? And sympathetic/parasympathetic?
- Is the visceral nervous system the same as the autonomic?
- For the neuron itself, myelinated vs unmyelinated, which nerves are which?
Can someone draw me a tree? Even in text. I'm using little coloured sticky notes and they don't fit anymore 😅
8 answers & replies
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[+][–]Pooja Iyer12thSample· 1mo ago
Tree time, I love a tree 🌳
Neural system
- CNS: brain + spinal cord
- PNS: all the nerves
- Afferent (sensory): tissues/organs → CNS
- Efferent (motor): CNS → tissues/organs
- Somatic: CNS → skeletal muscles (voluntary)
- Autonomic: CNS → involuntary organs and smooth muscles
- Sympathetic
- Parasympathetic
My mnemonic: Afferent = Arrives at the CNS, Efferent = Exits the CNS. And yes your sensory neurons sit under afferent only.
[+][–]Diya Menon11thSample· 1mo agoAuthor
Pooja the tree is going straight to a sticky note, you're a lifesaver 🌳✨
[+][–]Yash Tiwari11thSample· 1mo ago
Class 11 too, from what I understood the sympathetic and parasympathetic are in the CNS because they are automatic, the brain handles them. And the visceral nervous system is a separate third system, so the human neural system = CNS + PNS + visceral. Right?
[+][–]Kavya NaikDropperSample· 1mo ago
Yash, a small fix. CNS is only the brain and the spinal cord, that's all. The sympathetic and parasympathetic are the two divisions of the autonomic neural system, and the autonomic is part of the PNS (specifically the efferent side). They carry the signals out from the CNS, but they are not in the CNS.
And the visceral nervous system isn't a third separate system. NCERT defines it as the part of the PNS comprising the nerves, fibres, ganglia and plexuses by which impulses travel from the viscera (the internal organs) to the CNS and from the CNS to the viscera. So it's more of a "viscera-side" description of the PNS, not a third box on the tree. Diya, add it as a note beside the PNS, not as a new branch.
[+][–]Diya Menon11thSample· 1mo agoAuthor
omggg the "viscera-side description" thing is exactly what I needed, I kept looking for it on the tree. Thank you Kavya didi!!
[+][–]Yash Tiwari11thSample· 1mo ago
oh ok mera galat tha, thanks didi, notes me CNS = sirf brain + spinal cord likh diya 🙏
[+][–]Ishita GoyalDropperSample· 1mo ago
Doubt 4, the neuron part. A neuron has three parts: the cell body (cyton), dendrites and the axon. Based on the number of axons and dendrites, we have:
- multipolar (one axon and two or more dendrites; found in the cerebral cortex)
- bipolar (one axon, one dendrite; found in the retina)
- unipolar (cell body with one axon only; embryonic stage)
Axons can be myelinated or unmyelinated. Myelinated nerve fibres are enveloped with Schwann cells that form a myelin sheath around the axon, and the gaps between the sheath are the nodes of Ranvier. They are found in spinal and cranial nerves. Unmyelinated fibres are enclosed by a Schwann cell that doesn't form the myelin sheath, and these are commonly found in the autonomic and somatic neural systems.
[+][–]Riya Singh12thSample· 1mo ago
Small thing that helped me: don't think of a nerve as one wire. A single spinal nerve usually has both sensory (afferent) and motor (efferent) fibres bundled together, so it's called a mixed nerve. The terms afferent/efferent describe the direction of one fibre's signal, not a whole nerve. So when you read "somatic" or "autonomic", imagine it as the motor side of a fibre going out to a particular type of target.
CNS is the head office, PNS is the roads and delivery vans. 🚚
