nervous system 🧠

Study Notes

Sensitivity refers to the ability of organisms to react to stimuli in the environment.
A stimulus triggers a reaction known as a response.

The human nervous system regulates bodily functions and interactions with the environment.
Voluntary actions are consciously controlled; involuntary actions operate without conscious control (e.g., heartbeat, breathing).

Central Nervous System (CNS) includes the brain and spinal cord.
- The spinal cord mainly handles automatic reflex actions.
- The brain processes sensory information from touch, smell, and taste.
Peripheral Nervous System (PNS) comprises cranial and spinal nerves, as well as sensory organs.
- Sensory organs actuate nerve impulses in response to stimuli.

Nervous tissue comprises nerve cells called neurons.
Each neuron consists of a cell body with a nucleus and nerve fibers (cytoplasmic strands).
- Sensory Neurone: Transmits impulses from sense organs to the CNS, featuring a circular cell body and a long nerve fiber.
- Relay Neurone: Relays impulses between sensory and motor neurons, typically located in the CNS with many short nerve fibers.
- Motor Neurone: Sends impulses from the CNS to effectors, characterized by an irregular-shaped cell body and a long nerve fiber.

A synapse is the junction between two neurons.
Nerve impulse transmission across a synapse relies on chemicals, as impulses cannot cross directly.
Painkillers can block these synaptic spaces, preventing the transmission of nerve impulses.

Sensation: Involves sensory and relay neurons; the brain interprets nerve impulses for sensations (e.g., feeling temperature).
- Pathway: Receptor → Sensory Neurone → Relay Neurone → Brain.
Voluntary Action: Involves relay and motor neurons; initiated by conscious decision (e.g., raising a hand).
- Pathway: Brain → Relay Neurone in spinal cord → Motor Neurone → Effector (muscle).

A reflex action is an automatic response to a stimulus without conscious thought.
Types of reflexes:
- Cranial Reflexes: Controlled by the brain (e.g., blinking).
- Spinal Reflexes: Governed by the spinal cord (e.g., withdrawing hand from heat).
Reflex Arc: The pathway for reflex actions, involving receptors, sensory neurons, relay neurons, motor neurons, and effectors.

Similarities: Both systems transmit messages to target organs in response to stimuli.
Differences:
- Nervous control is localized; endocrine control can affect multiple organs via hormones.
- Nervous control elicits quick responses; endocrine responses are slower.
- Nervous responses can be voluntary, involuntary, short-lived; endocrine responses are usually involuntary and can be long-lived.