CNS-sensory/Motor Flashcards
Major Divisions of the nervous system
- Afferent (sensory input) : cell bodies out of CNS
- Cranial Nerves: somatic, visual, olfactory, taste, auditory
- Spinal Nerves: Somatic Sensation Touch, Temperature, Pain
- Efferent(motor output): cell bodies in CNS
- Cranial Nerves
- Spinal Nerves
- Somatic Efferent: Innervates skeletal muscle, only excitatory (ACh), Motor Neurons
- Autonomic efferent: innvervates interneurons, Smooth and cardiac muscle, Excitatory and inhibitory.
- Enteric
Brain Anatomy
- Cerebrum (cortex) : frontal, central sulcus, parietal, lateral sulcus, occipital temporal
- Corpus Callosum
- Thalamus
- Brainstem: midbrain, pons, medulla
- Cerebellum
Divisions of the Spinal Cord
-Cervical nerves (8 pair): neck, shoulders, arms, and hands
-Thoracic Nerves(12 pairs): shoulders, chest, upper abdominal wall
-Lumbar nerves(5 pairs): lower abdominal wall, hips, and legs
Sacral Nerves (5 pairs): genitals and lower digestive track
-Coccygeal nerves (1 pair)
Early development of the Nervous system
Fertilized egg (ovum) –> ball of cells –> Blastocyst (week 1) –> Blastocyst (week 2) –> Blastocyst (week 3) : inside is the embryonic disk + neural plate
The neural tube
- vesicles develop during week 4
- forebrain
- midbrain
- hindbrain
The forebrain becomes?
Cerebral hemispheres + thalamus
The midbrain becomes?
Midbrain
The hindbrain becomes?
Cerebellum: pons + medulla
Ventricles
- space between the tissues of the brain.
- contain 150 mL of cerebral spinal fluid
Formation of cerebrospinal Fluid
-produced by the choroid plexus ( in the four ventricles, but mainly the two lateral) at a rate of 500 mL/day
Function of cerebrospinal Fluid
- Supports and cushions the CNS. Specific gravity of CSF and the brain are equal
- Provides nourishment to the brain
- Removes metabolic waste trhough absorption at the arachnoid villi.
Composition of cerebrospinal Fluid
-sterile, colorless, acellular fluid that contains glucose
Circulation of cerebrospinal Fluid
-passive (not pumped)
3 meninges(membranes) of the CNS
- cover the brain and spinal chord
-
How does the CSF returned to the blood
returns via the dural sinus
Characteristics about the blood supply to the brain
- glucose is usually the only substrate metabolized by the brain
- very little glycogen in the brain
- Brain needs a continous supply of glucose and oxygen (glucose transport into the brain does not require insulin)
- A few seconds of blood supply interruption can lead to loss of consciousness. A few minutes can lead to neuronal death (stroke)
- Brain receives 15% of total blood (but 2% of total mass)
Path of blood from the heart to the brain
heart –> Aorta –> either brain or body (85%) –> Vertebral or Common carotid artery –> Internal Carotid Artery (base of the brain) or External Carotid Artery (outside of the head).
Path of Cerebral Circulation: CSF and blood
CSF –> Choroid Plexus –> ventricles –> subarachnoid space –> arachnoid villi –> dural sinus –> venous system –> heart –> Carotid Arteries or Vertebral arteries –> circle of willis –> brain –>Venous –> heart.
Blood-brain barrier (capillary wall)
- tight junctions between endothelial cells
- impermeable to plasma proteins and large organic molecuels
- permeable to Water, CO2, O2, Lipid-soluble substances, Na+, K+, Cl -
- active transport of glucose and some amino acids
Senesation
awareness of sensory stimulation
perception
the understanding of a sensations meaning
Law of specific nerve energies
regardless of how a sensory receptor is activated, the sensation felt corresponds to that of which the receptor is specialized
Law of projection
regardless of where in the brain you stimulate a sensory pathway, the sensation is always felt at the sensory receptors location
Modality
General class of a stimulus
Labeled-line
the brain “knows” the modality and location of every sensory afferent
How Sensory Receptors work
- Stimulus energy –> adequate stimulus(specificity)
- Receptor membrane
- transduction
- Ion channel activation
- Afferent (signal sent to brain)
Acuity
ability to differentiate one stimulus from another
Receptive field (RF)
The region in space that activates a sensory receptor or neuron
Lateral inhibition
- 2 order neurons send signal via interneurons to decrease the intensity of a stimulus.
- helps localize a stimulus
Touch: Mechanoreceptors:
specialized end organs that surround the nerve terminal. These organs allow only selective mechanical information to activate the nerve terminal
Superficial Layers
Meissner’s Corpuscle: fluid-filled strucutre enclosing the nerve terminal, Rapidly adapting. Light stroking and fluttering
Merkel Disk: small epithelial cells surround the nerve terminal. Slowly adapting, pressure and texture
Deep Layers
Pacinian Corpuscle: Large capsules of connective tissue surround the nerve terminal. Rapidly adapting, strong vibrations
Ruffini endings: Nerve endings wrap around a spindle-like structure. Slowly adapting, stretch and bending of skin.
proprioception
muscle spindles provide sense of static position and movements of limbs and body
How are mechanoreceptors activated
by stretching the cytoskeletal strands.
