Lecture 2

Flashcards about Central Control of Somatosensory Information

Central Control of Somatosensory Information

Sensory signals are subject to modification before they reach higher levels of the CNS; this modification can come from inhibition from collaterals, pathways descending from higher centers, synapses on axon terminals, or indirectly via interneurons.

Role of Cortex in Afferent Information

The cortex provides inhibition to sensory fibers and projection neurons, effectively reducing the effect of a stimulus.

Inhibitory Effect of Cortex

Removal of this effect of the cortex will result in amplification of your response to sensory input.

Lateral inhibition

Sensory information can be gated by the CNS

Afferent Neuron

Different branches of the sensory receptor are located in the skin

Anterolateral system (spinothalamic tract)

Carries pain, or hot/cold information up to the somatosensory cortex

Dorsal column system

Carries information on fine touch mechanoreception to the somatosensory cortex

Painful Stimulus

Exposure to a painful stimulus activates free neuron endings (sensory receptors that respond to pain).

Anterolateral System - First Synapse

First synapse is located in the dorsal horn of the grey matter of spinal cord on same side of body which was stimulated

Anterolateral System - Crossover

Secondary neuron crosses over to the other side of the CNS at the level of the spinal cord

Anterolateral System - Second Synapse

Secondary neuron synapses with projection neuron in the thalamus which travels to somatosensory cortex

Dorsal Column System - Activation

A tap on the right shoulder generates action potentials in mechanoreceptors in the right shoulder.

Dorsal Column System - First Synapse

First synapse between the sensory neuron and the secondary neuron is in the brainstem

Dorsal Column System - Crossover

Secondary neuron crosses over to the other side of the CNS at the level of the brainstem

Dorsal Column System - Second Synapse

Secondary neuron synapses with projection neuron in the thalamus which travels to somatosensory cortex

Somatosensory Cortex Pathways

Both pathways end in the somatosensory cortex on the contralateral side of the body.

Somatosensory Cortex

All sensory information (ie. pain or fine touch) goes from the thalamus to the somatosensory cortex

Location of the Somatosensory Cortex

The somatosensory cortex is located behind the motor cortex and the central sulcus

Body Mapping in Somatosensory Cortex

Different regions of the body are represented by regions in the somatosensory cortex of different size.

Photoreceptors

Photoreceptors in the eye, or the sensory cells, are depolarized at rest and hyperpolarized when activated

Optical component

Responsible for focusing the visual image on the receptor cells

Neural component

Transforms the visual image into a pattern of graded potentials and action potentials

Cornea

Where the sclera becomes clear at the very front, or the anterior surface, of the eye; responsible for refracting light waves

Iris

Regulates the size of the pupil and amount of light entering eyeball; gives your eyes colour

Lens

Behind the iris; works with the cornea to focus the visual image on the retina

Retina

Located behind the lens, against back of the eye; where the photoreceptors are found

Rods

Activated in very low light conditions and are monochromatic

Cones

Activated when there is more light present and are responsible for colour vision

Optic nerve

Leaves through the back of the eyeball towards the thalamus and the cortex; made of axons of retinal ganglion cells

Aqueous humour

A gelatinous fluid that fills the space between the lens and the cornea

Vitreous humor

A gelatinous fluid found behind the lens

Refraction

Change in direction ie. Bending

Presbyopia

Loss of elasticity of the lens resulting in the inability to accommodate for near vision; due to the breakdown of the ciliary muscles; age-related

Myopia

Nearsightedness

Hyperopia

Farsightedness

Astigmatism

Oblong shape of the eyeball is the problem

Glaucoma

Damage to the photoreceptors due to increased intraocular pressure

Cataracts

Clouding of the lens

Interneurons

Three different types of interneurons: horizontal, bipolar and Amacrine cells

Bipolar cells

Interneurons which take information from the photoreceptors to the retinal ganglion cells

Cones - Dark Environment

When light is not present an enzyme converts GTP into cyclic GMP (cGMP; cyclic guanosine monophosphate)

Cones - Light Environment

When light hits the photopigment, retinal changes conformation from cis to trans conformation; this change in conformation activates a molecule called cyclic GMP phosphodiesterase

OFF bipolar cell

Activated by glutamate

ON bipolar cell

Inhibited by glutamate

No light present

Action potentials generated in the OFF pathway but not in the ON pathway

Light present

ON pathway is activated due to the release of the inhibition on the ON bipolar cell by glutamate