Chapter 12 - Peripheral Nervous System Flashcards Preview

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Name the 12 cranial nerves

Spinal accessory


spinal reflex actions

It is defined as an involuntary action performed by muscles under the direction of the spinal cord in response to the stimulus. The best example of the reflex action is pulling of hand when we touch hot or very cold objects and contraction of the pupil when the light is shown in the eye.


spinal reflex arc

The path which is followed by impulses during the reflex action is called the reflex arc. It consists of an afferent (or sensory) nerve, usually one or more interneurons within the central nervous system, and an efferent (motor, secretory, or secretomotor) nerve.


dual innervation of the ANS

fight or flight

released chemical signals into the blood that effect organs and tissue differently from the same chemical signal.

hair follicles contract and hair stands up
sweat glands contract and squeeze out sweat
Alveolar relax and expand
heart muscles beat faster
shut down digestive system
dilate/constrict blood vessels

The same chemical released into blood makes each organ respond in their unique way to the same stimulus.


Types of sensory recpetors


Mechanoreceptors - tactile receptors, baroreceptors, proprioceptors






These respond to chemicals in solution



These respond to mechanical forces such as pressure, touch, stretching and vibration


Mechanoreceptors - tactile receptors

Sense pressure, touch and vibration.


Mechanoreceptors - barorreceptors

Detect pressure changes in blood vessel walls and in areas of the urinary, reproductive and digestive tracts.


Mechanoreceptors - proprioceptors

Sense positions of skeletal muscles and joints, and tension in the ligaments and tendons.



These respond to stimuli that may be damaging such as extreme heat or cold, excessive pressure and inflammatory chemicals resulting in pain.

Common in superficial skin, around blood vessel walls, inside joint capsules and inside periostea of bones.

Carried on two types of fibers called type A (myelinated, carry fast pain sensations) and type C fibers (carry slow pain that feels like aching and burning)



Respond to light. For example the receptors in the retina of the eyes.



Respond to temperature changes

Are ‘free nerve endings’ in the dermis, liver, skeletal muscles and hypothalamus.

3 or 4 times more cold to warm receptors.

Are phasic receptors that quickly adapt to stable temperatures


Samatosensory system - sensations and perception

Sensation is the awareness of environmental changes, internally and externally.

How we interpret these changes is called perception.

How we respond to sensations is determined by our perceptions of them.


Somatosensory system

Serves the limbs and wall of the body.

Inputs are received from exteroceptors, interoceptors and proprioceptors.

Transmits information about various sensations.

The sensory receptors make up the receptor level, where as the processing in the ascending pathways makes up the circuit level of the somatosensory system. The processing in the cortical sensory areas is called its perceptual level.

For sensations to occur, stimuli must excite a receptor and action potentials must reach the CNS.


Somatosensory system - sensory neurons

Tonic receptors - always active. The rate at which action potentials are generated changes when stimulus increases or decreases.

Phasic receptors - normally inactive but become active for a short period when a change occurs in the conditions they monitor.

These receptors provide information about intensity and rates of change of a stimulus.


somatosensory system - Adaptation

Adaptation is a reduced sensitivity, whereas a stimulus is consistently present. Peripheral adaptation occurs as levels of receptor activity change. The initial strong response subsides over time, partly because the size of the generator potential increases gradually. This is typical of phasic receptors, and for this reason, they are also called fast adapting receptors. The tonic receptors are called slowly adapting receptors because they show little peripheral adaptation. Pain receptors or nociceptors are examples of slow adapting receptors.


Arrangement of sympathetic and parasympathetic neurons and ganglia

Sympathetic Nerve fibres originate from the thorocolumbar area of the spinal chord. pre ganglionic fibres tend to be shorter and closer to the spinal chord. Fibres come out of a ganglion and post ganglionic sympathetic fibres are longer, branching out to multiple effectors which get activated simultaneously.

Parasympathetic nerve fibres are craniosacral (sprout from the base of the brsin and sacrum. preganglionic fibres are long and project to and synapse with the postganglionic fibres in a ganglion that is close to the target organ. Post ganglionic fibres of the parasympathetic are short, just long enough to reach their effector. communicates with the organs and glands they effect one on one.



Singular ganglion

Ganglia is the plueral


Sympathetic nervous system

Stimulus received. Then CNS Sends an action potential down spinal chord to preganglionic neuronal axons. Flowing to the ganglia. Those axons then release neurotransmitter ACH (acetylcholine). If threshold is reached at the ganglion it can stimulate several neurons at the same creating action potentials in the post ganglionic nerve fibres.

Norepinephrine is Then released as a neurotransmitter by all sympathetic post ganglionic nerves onto effectors.

Hormones - preganglionic nerves also go directly to adrenal glands (no ganglia involved or post ganglionic nerves) and release ACH. Triggering the adrenal medulla to release norepinephrine and epinephrine. This then stimulates effector organs like blood vessels to expand and contract depending on their location in the body (what type of receptors the effectors have alpha/beta) and if the organs they serve will be required in the emergency situation or not.


Parasympathetic nervous system

Nerves are craniosacral. Cranial nerves dont run through the spinal chord and vary the types of neurons they contain. Not all are autonomic motor fibres. Some cary voluntary fibres and others sensory fibres. Some cranial nerves contain both motor and sensory neurons.

ACH at ganglion and effector


2. Optic nerve

Sensory neurons make this nerve.

Takes visual information gathered by the eyes and sends it to the brain.


3. Oculomotor nerve

Motor nuerons make this nerve

Controls four of the six muscles that control the movement of your eyes.


9. Glossopharyngeal nerve

Contains both motor and sensory neurons to make the nerve.

Leads to your tongue and your pharnyx


10. Vagus nerve

Both motor and sensory neurons make this nerve

Controls the heart and digestive tract among other functions.

Mostly involuntary motor fibres.

When you eat stomach sends signals to the brain through sensory nerves telling the brain that its full. Brain sends signals down the vagus nerve slowing down heart rate, storing glucose and reducing norepinephrine. makes you feel relaxed.