Nervous System: Somatic System

Somatic Nervous System

Responsible for conscious perception and the resulting voluntary response via the skeletal system (movement).

Type of sensory receptors

• Light

• Heat

• Sound

• Pressure

• Chemical Changes

Sensation

The activation of sensory receptors

Perception

The processing of sensation into a meaningful pattern

Relationship between sensation and perception

Perception occurs from sensation.

But, not all sensation is perceived.

Transduction

The conversion of energy from sensations into electrochemical signals that travel through the nervous system.

Is what we perceive reality?

No, as our body does not have the receptors to perceive all forms of reality such as magnetic forces, polarised light waves, X-rays, etc.

Photoreceptors

Senes visible wavelengths of light

Mechanoreceptors

Sense vibration, sounds, proprioception, movement, stretching

Thermoreceptors

Sense too low or too high temperatures

Osmoreceptors

Sense changes in solute concentrations within the body

Noicireceptors/pain receptors

Sense chemicals released from tissue damage (pinching/burning sensation)

Chemoreceptors

Senses smells and taste, Oxygen (O2) and carbon dioxide (CO2)

Compound Sensations

Sensations that arise from a combination of many receptors

• E.g Wetness: mechanoreceptors (feeling water), thermoreceptors (feeling the temperature of water)

Special Senses

Senses that have specialised organs

• Tongue - Taste

• Nose - Smell

• Eyes - Sight

• Ears - Hearing

• Ears - Balance/Equilibrium

General Senses

Senses that are distributed through the entire body

Voluntary Sensations:

• Touch & Pressure

• Posture & Movement

• Temperature

• Pain

Involuntary Sensation:

• Visceral Sense (e.g blood glucose levels, blood pressure)

  • Can be felt if the sensation is strong enough (e.g breathing in cold air)

Afferent pathways to the brain

There are multiple afferent pathways of nerves that send electrical impulses (information) to the brain for different sensation.

• Electrical impulses/signals/information will always cross over to the opposite side of the body through the nervous system either when the electrical signal enters the spinal cord or the brain stem.

Where are sensations processed within the brain?

In the parietal lobe, specifically the somatosensory cortex

Sensory Homunculus (Little Man)

Indicates that the somatosensory cortex does not equally process information from all parts of the body.

Areas such as the hands, face, tongue and genitalia have a larger proportion of the somatosensory cortical processing reserved for them as they are the most sensitive parts of the body.

How are motor neurons activated?

A signal is sent from the primary motor cortex, travelling down an efferent pathway (crossing over either at the brain stem or when exiting the spinal cord), then reaching and activating the motor neurons at the designated skeletal muscles.

What part of the brain activates motor neurons for movement?

The primary motor cortex, located within the frontal lobe.

Motor Homunculus (Little Man)

Indicates that the primary motor cortex does not equally send signals all parts of the body.

Areas such as the hands and face, have a larger proportion of the primary motor cortex reserved for them as they can perform complex and finer movements such as speech.