Pacinian corpuscle and the heart

structure of the Pacinian corpuscle

Sensory neurone ending, wrapped in layers of connective tissue, called lamellae

what type of receptors are Pacinian corpuscles

mechanoreceptors - they detect mechanical stimuli - pressure and vibrations

How does the Pacinian corpuscle generate an electrical impulse

• Pressure causes the deformation of the lamellae - layers of connective tissue - around the sensory neurone ending

• This causes deformation of the stretch-mediated sodium ion channels, and they open

• Allowing the entry of sodium ions into the neurone (by facilitated diffusion)

• This causes depolarisation and creates a generator potential

• If this is high enough to reach threshold, an action potential is generated

What are rod cells sensitive to 

light intensity 

what are cone cells sensitive to and where are they found

sensitive to different wavelengths of light, concentrated in the fovea

How do rods and cones detect light 

• Light causes the chemical breakdown of optical pigments inside the rods and cones (rhodopsin in rods and iodopsin in cones)

• This breakdown alters the permeability of the plasma membranes and triggers a generator potential 

• If this reaches threshold, an action potential is formed in the bipolar neurone 

• The electrical impulse travels to the brain via the optic nerve 

Rod cells sensitivity to light

very sensitive to light, since multiple rod cells connect to a single bipolar cell, meaning that many weak generator potentials together can trigger a nerve impulse in the bipolar cell

Cone cells sensitivity to light 

less sensitive to light, since each cone cell is connected to its own bipolar cell, so the generator potential from an individual cone cell must be higher, in order to trigger a nerve impulse in the bipolar cell

How are cones sensitive to different wavelengths of light

cone cells are either red-sensitive, blue-sensitive or green-sensitive

what is visual acuity

the ability to distinguish between two separate points when viewing an image

rods vs cones visual acuity 

• Cone cells have a higher visual acuity 

• Multiple rod cells are connected to a single bipolar cell, so the brain is not able to determine which impulses have been generated by which specific rod cell, so information from many neighbouring rod cells is detected as a single point

• However, each cone cell is connected to its own bipolar cell, so the brain can interpret the information from each cone cell as separate points in an image

Type of stimulation of the heart 

myogenic - impulses are generated in the muscle tissue, and not from the nervous system 

sinoatrial node (SAN)

group of cells in the wall of the right atrium, aka pacemaker 

atrioventricular node (AVN)

conductive tissue that links the atria and the ventricles

bundle of His

conductive fibres that carry waves of depolarisation down the septum to the base of the ventricles

Purkyne tissue 

conductive fibres that carry waves of depolarisation from the base of the ventricles into the ventricle walls 

Process of myogenic stimulation of the heart 

• The SAN initiates the heartbeat by initiating a wave of electrical activity which passes across the atria - so the atria contract from the top down 

• After a short delay, which allows the atria to empty before ventricular contraction, the AVN relays the electrical activity

• Down the bundle of His to the Purkyne tissue - this causes the ventricles to contract from the base upwards

how does exercise cause an increase in heart rate 

• Rate of respiration of muscle cells increases to release more ATP for muscle contractions 

• This means the concentration of carbon dioxide in the blood increases

• Chemoreceptors on the walls of the aorta and the carotid artery detect this change

• They increase the frequency of the electrical impulses to the centre of the medulla oblongata that increases heart rate

• This increases the frequency of electrical impulses through the sympathetic pathway to the SAN, so increases heart rate