Physiology 3120 Lecture Notes - Lecture 23: Locus Coeruleus, Alpha Motor Neuron, Resting Potential
15 May 2018
School
Department
Course
Professor
Lecture 23 – Consciousness, Evoked Potential, EEG, Sleep
Consciousness
- Definition – Awareness of environment and oneself
- Two aspects of consciousness:
o 1. Content of consciousness: e.g., memory, perception, attention
o Involves the cerebral cortex and the things going on there
o 2. Level of consciousness: e.g., awake, alert, asleep, coma
o Depends on the brainstem (neurons project in rostral pons/caudal midbrain)
- Old idea about consciousness: Ascending Reticular Activating System
- Brainstem: medulla, pons, midbrain
- In pioneering experiments:
o Animal with electrodes implanted in certain parts of the brain stem:
o If they gave small pulses of electricity to stimulate at low levels, they could wake up
a sleeping animal
- If a lesion is made at the top end of the brainstem, and the cerebral hemispheres are
removed, the animal will stay in a good condition because cardiovascular and respiratory
centers are located in the brainstem = animal will be in coma
- If there is a decerebration (bilateral lesion – on both sides), the animal will be unconscious
o = there is ascending system coming from the reticular formation
- Ascending signals come up from the region (where the green area is)
o If you stimulate there, you can wake up a sleeping animal
- There are descending pathways from the reticular formation
o Reticulospinal axons sending IPSPs to alpha motor neurons of proximal muscles
o In REM sleep, proximal muscles are inhibited through descending pathways of the
brainstem
find more resources at oneclass.com
find more resources at oneclass.com
Conscious arousal system
- In the brain stem
o Caudal: down at the spinal cord end
o Rostral: at the top of the brain towards the cerebral hemispheres and cerebral
cortex
- There are neurons coming from this region called arousal neurons
Ascending arousal system
- Ascending arousal system is in the brainstem: rostral pons/caudal midbrain area
- There are a number of systems of neurons that originate in this area of the brain that
control consciousness (person is awake and attentive)
- Noradrenergic system (locus ceruleus)
o Nucleus of origin of axons in the system is called the locus ceruleus
o Nucleus sends axons to all areas of the brain
o Thousands of axons go to different areas of the brain, including widespread areas of
the cerebral hemispheres and even the cerebellum
- Transmitter in the system is norepinephrine/noradrenaline
- Noradrenergic system has
o 1. Widespread connections
o 2. Alters membrane potentials
o 3. Produces depolarization of neurons in the cerebral cortex = puts them in the
awake state
▪ Moves resting membrane potential closer to threshold so if any other signals
come into the neuron, it will be ready by being depolarized = neurons may
fire for an incoming excitatory input
find more resources at oneclass.com
find more resources at oneclass.com
Ascending arousal system
- There are MANY systems all of which come from the same area in the brainstem
o All have different transmitters
o There are nuclei that send axons to a variety of different areas in the cerebral
hemispheres where they produce different effects
- Noradrenergic (Locus Ceruleus): Cortical attention
- Serotonergic (Raphe Nuclei): Failure to cause arousal in SIDS (sudden infant death
syndrome)
o 5 hydroxy’ triptamine: serotenergic transmitter
o In SIDS, in 50% of cases there is a lack of development in this area of the brain
o = can cause SIDs
- Dopaminergic: associated with reward based learning, addiction
o Wide spread – goes to many different areas including the cerebral cortex and the
limbic system
- Histaminergic: Anti-histamines cause drowsiness
- Cholinergic: associated with Alzheimers disease
o Widespread system from the basal ganglia to the cerebral cortex
- All systems are involved in cooperative interplay
o Cooperate together to achieve different levels of consciousness
- E.g. achieve different states of sleep, getting out of sleep and back to normal consciousness
Coma: absence of consciousness
Two different ways to get a coma
1. Bilateral lesion of Cerebral Cortex
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 23 consciousness, evoked potential, eeg, sleep. Definition awareness of environment and oneself. Involves the cerebral cortex and the things going on there: 2. Level of consciousness: e. g. , awake, alert, asleep, coma: depends on the brainstem (neurons project in rostral pons/caudal midbrain) Old idea about consciousness: ascending reticular activating system. In pioneering experiments: animal with electrodes implanted in certain parts of the brain stem: If they gave small pulses of electricity to stimulate at low levels, they could wake up a sleeping animal. If there is a decerebration (bilateral lesion on both sides), the animal will be unconscious: = there is ascending system coming from the reticular formation. Ascending signals come up from the region (where the green area is) If you stimulate there, you can wake up a sleeping animal. There are descending pathways from the reticular formation: reticulospinal axons sending ipsps to alpha motor neurons of proximal muscles.
