Download Objectives 38 - U

1. Somatic system
Primary afferents – sensory info reaches CNS via central processes of primary sensory neurons
(most are large); cell bodies in PNS dorsal root ganglions and peripheral process which is itself
sensitive to some kind of stimulus (mechanoreceptive endings) or receives inputs from
specialized receptor cells (cochlear air cells); exceptions includes rods/cones and olfactory
receptor cells
Motor neurons – somatic LMNs have cell bodies in CNS (anterior horn) and axons that
innervate skeletal muscle
Visceral system (autonomics)
Primary afferents – visceral primary afferents (most are small) have cell bodies in spinal or
cranial nerve ganglia; sympathetic  thoracolumbar; parasympathetic  craniosacral
Motor neurons – some can be hormonal; 2-neuron chain starting from preganglionic neuron in
CNS that synapses on a postganglionic neuron (in periphery); sympathetic preganglionics are
located in thoracic and upper lumbar spinal cord, and postganglionics are located in chain
ganglia or prevertebral ganglia; parasympathetic preganglionics are located in a series of
brainstem nuclei and in sacral spinal cord, and postganglionics are located in ganglia near
viscera
2. Visceral sensory info within CNS
- visceral afferents reach the spinal posterior horn (or nucleus of the solitary tract if arriving
in brainstem)  feed into reflex arcs, pathways ascending to cerebrum, and to the cerebellum
- after a relay in the thalamus (VPM)  primary visceral sensory cortex in insula  visceral
association cortex (insula, orbital cortex, cingulate gyrus)
- hypothalamus receives ascending information and is the major source of descending
pathways; hypothalamic output is modulated by limbic cortex and amygdala
3. Brainstem visceral network
- interconnected set of brainstem nuclei play a role in ascending and descending visceral
pathways; ascending involves parasympathetic sensory info
- Nucleus of the solitary tract: site where gustatory and visceral afferents terminate  NST
conveys this info to reflex circuits (nucleus ambiguus) and other brainstem visceral network
areas
- Ventrolateral part of medullary reticular formation  controls arterial blood pressure
through descending projections to preganglionic sympathetic neurons in the spinal cord;
projections from nucleus of solitary tract to this region of the reticular formation form the
basis of the baroreceptor reflex – control of cardiovascular, respiratory, and other visceral
functions; pontine micturition center
- parabrachial nuclei – near superior cerebellar peduncle in rostral pons; site at which spinal
and vagal (sympathetic, parasympathetic) info is integrated and forwarded to hypothalamus,
amygdala, and thalamus; these nuclei receive both visceral inputs from the nucleus of the
solitary tract and visceral, thermoreceptive, and nociceptive inputs from most superficial layer
of the spinal posterior horn (lamina I)
- Periaqueductal gray around cerebral aqueduct; contains longitudinally oriented columns of
neurons that mediate behavior patterns (modulation of pain, defensive posture); ascending and
descending sympathetic info
4. Role of hypothalamus and amygdala in maintenance of homeostasis and control of driverelated behavior
Hypothalamus
- hypothalamus is a nodal point in neural circuits underlying drive-related behaviors
- interconnections with visceral parts of nervous system  control of blood glucose/pressure,
body temperature
- interconnections with limbic structures  awareness of homeostatic needs (I’m hot)
- control of pituitary gland
Inputs
- visceral nuclei in brainstem and spinal cord  keep hypothalamus updated on internal
condition of body
- limbic structures like hippocampus, amygdala, and septal nuclei; limbic inputs arrive by way
of the fornix (from the hippocampus), the medial forebrain bundle (from septal nuclei);
collectively, they keep the hypothalamus updated on other aspects of the environment
- inputs also reach hypothalamus from retina and direct physical stimuli; axons of some retinal
ganglion cells terminate in suprachiasmatic nucleus on each side of anterior hypothalamus 
master clock for circadian rhythms (sync with 24-hour day)
- some hypothalamic neurons are sensory receptors responsive to temp, blood osmolality,
chemical concentrations in blood
Outputs
- hypothalamic connections with visceral nuclei and limbic structures are reciprocal
- some descend through the brainstem  nucleus of solitary tract, dorsal motor nucleus of
vagus, intermediolateral cell column of spinal cord
- projections through the medial forebrain bundle  septal nuclei, amygdala, other limbic
structures  affecting was goes on in the cortex
Amygdala
- collection of nuclei located in temporal lobe at anterior end of hippocampus; role in linking
conscious feelings with emotional expression
- divided into central, basolateral, and corticomedial nuclei
- central nucleus is connected with hypothalamus and brainstem visceral network; it receives
inputs from the basolateral nucleus; key structure in mediating emotional responses
-basolateral nucleus is interconnected with limbic and sensory cortices and the thalamus;
provides outputs to central nucleus; key structure in recognizing emotional significance of
objects/events
- corticomedial nucleus gets inputs from the olfactory bulb; it sends outputs to the olfactory
bulb and hypothalamus
5. Role of basal ganglia in control of drive-related behavior
- forebrain components of the basal ganglia are striatum (putamen, caudate nucleus, nucleus
accumbens), globus pallidus, and subthalamic nucleus; modulatory inputs come from
dopaminergic neurons in substantia nigra and ventral tegmental area
- striatum receives inputs; globus pallidus (GPi) which receives a balance of
excitatory/inhibitory inputs sends inhibitory outputs; circuit: cortex  striatum  globus
pallidus  thalamus  cortex loop
- excitatory inputs from subthalamic nucleus to the globus pallidus
- of importance for drive-related behavior is the circuit involving hippocampus, amygdala,
limbic cortex to ventral striatum (nucleus accumbens, caudate, putamen)  ventral pallidum
(part of globus pallidus ventral/inferior to anterior commissure)