Neurophysiology II Flashcards
Week 3
Understand components of the afferent and efferent divisions of the nervous system
The afferent and efferent divisions of the nervous system are distinguished by the direction in which signals travel through the nerves:
Afferent
Also known as the sensory division, this division carries signals away from a stimulus to the central nervous system (CNS). Afferent nerves carry information from the skin, muscles, joints, and visceral organs.
Efferent
Also known as the motor division, this division carries signals from the CNS to the muscles and glands of the body. Efferent nerves innervate skeletal, cardiac, and smooth muscle, as well as glandular tissue and secretory cells.
The efferent division is further subdivided into the somatic nervous system and the autonomic nervous system:
Somatic nervous system
Also known as the voluntary nervous system, this division supplies motor impulses to the skeletal muscles.
Autonomic nervous system
Also known as the involuntary nervous system, this division supplies motor impulses to cardiac muscle, smooth muscle, and glandular epithelium. The autonomic nervous system is further subdivided into sympathetic and parasympathetic divisions.
Describe a simple reflex arc
A simple reflex arc is a neural pathway that automatically allows the body to respond to a stimulus without the brain’s involvement. The components of a reflex arc are:
Receptor: A sensory cell that detects a change in the environment or stimulus
Sensory neuron: Carries electrical impulses from the receptor to the spinal cord
Interneuron: Also known as an adjustor, this cell connects the sensory neuron to the motor neuron
Motor neuron: Carries electrical impulses from the interneuron to the effector
Effector: Produces the response to the stimulus, such as a muscle-contracting
Here’s an example of a simple reflex arc in action:
1. You touch something hot
2. The receptor in your skin detects the change in temperature
3. The sensory neuron sends electrical impulses to the spinal cord
4. The relay neuron in the spinal cord connects to the motor neuron
5. The motor neuron sends electrical impulses to the effector
6. The effector, in this case, a muscle, contracts to move your hand away
Other simple reflexes include blinking when your cornea is touched or salivating when you see food.
Explain the role of sensory receptors and differences in sensitivity
Sensory receptors provide the CNS with information about our internal and external environments
- Sensation = arriving information
- Perception = awareness of sensation
Our sense can be divided into two groups:
General senses
- Temperature, pain, touch, pressure, vibration, proprioception
- Covered in Module 3.2
Special senses
- Olfaction (smell), gustation (taste), vision, hearing, equilibrium (balance)
Peripheral adaptation decreases the number of action potentials that reach the CNS.
Classify the general sensory receptors based on stimuli they sense
Chemoreceptors: Nerve cells that detect small changes in the concentration of chemicals/compounds.
Sensory neurons that are always active are called tonic receptors.
Compare and contrast general and special senses
There are 5 special senses
1. Olfaction
2. Gustation
3. Vision
4. Balance
5. Hearing
Compared to the general senses, special sense receptors are
generally more complex and localised for specific functions. General senses include touch, pain, temperature, proprioception, vibration, and pressure.
- General senses more widely distributed throughout body
- Basic principles of receptor function still apply
Briefly describe the structure and functions of olfaction.
Our sense of smell involves sensory receptors responding to airborne chemical stimuli
- Located in the nasal cavity
- Sense water-soluble and lipid-soluble substances (odorants)
Olfactory organs are made up of two layers
- Olfactory epithelium: Contains olfactory sensory neurons
- Lamina propria
Briefly describe the structure and functions of Gustation
Our sense of taste provides information about the food and liquids we consume
- Taste receptor cells (TRCs) located in taste buds
- Each taste bud contains 40-100 TRCs
- Stimulated by dissolved food molecules
- TRCs in tastebuds > synaptic transmission > sensory afferent fibres > CNS
Briefly describe the structure and functions of vision
Eyeball anatomy
Fibrous layer
~ Sclera: White of the eye
~ Cornea: Transparent layer (No blood vessels, oxygen/nutrients supplied by tears), free nerve endings
Vascular layer
~ Pigmented ring structure
~ Pupil = central opening of iris (Iris controls the amount of light entering through the pupil)
~ Contains blood vessels, pigmented cells, (smooth) pupillary muscles
~ Autonomic nervous system
- Sympathetic stimulation results in pupil dilation (e.g., dim light)
- Parasympathetic stimulation results in pupil constriction (e.g., bright light)
Inner layer (retina)
The inner layer (retina) contains two layers:
1. Pigmented layer
- Absorbs light, prevents reflection
- Supports function of neural layer
2. Neural layer
- Several layers of cells
- Contains photoreceptors (Photoreceptors transduce light into electrical signals: Rods & Cones)
- Transduction pathway (simplified): Photoreceptor > bipolar cell > ganglion cell > CNS
- Photoreceptor cells that are most useful in dim light are rods, while photoreceptor cells that convey our ability to see colour are cones.
Briefly describe the structure and functions of balance
Balance and hearing rely on intricate mechanisms within the inner ear
- Equilibrium senses head position (gravity, acceleration, rotation)
- Hearing detects sound waves
- Both senses rely on the inner ear
- Hair cells are mechanoreceptors
Hair cells are specialised sensory cells found in the vestibular system (i.e., utricle, saccule, and semicircular canals) and the cochlea of the inner ear. These cells play crucial roles in both balance (i.e., vestibular function) and hearing (i.e., auditory function).
Stereocilia transmit the movement of the tympanic membrane to the inner ear, helping convey information about the head’s rotational movements. When an external force bends the stereocilia of the inner ear hair cells, there is a change in the transmembrane potential of the hair cells.
The ear is divided into three anatomical regions:
- External ear
- Middle ear
- Inner ear
Briefly describe the structure and functions of hearing
Hearing is the perception of sound
* Sound consists of pressure waves conducted through a medium
The cochlear receptors that provide our sense of hearing are hair cells.
